Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $112.78   12.523%   $126.9034   $126.90   $126.90   $126.90  
  Purchase #2 $170.74   11.106%   $189.7024   $189.70   $189.70   $189.70  
  Purchase #3 $159.69   9.298%   $174.538   $174.54   $174.55   $174.50  
  Purchase #4 $130.97   11.477%   $146.0014   $146.00   $146.00   $146.00  
  Purchase #5 $192.81   13.537%   $218.9107   $218.91   $218.90   $218.90  
  Purchase #6 $132.99   11.641%   $148.4714   $148.47   $148.45   $148.50  
  Purchase #7 $247.77   7.522%   $266.4073   $266.41   $266.40   $266.40  
  7 purchase totals = $1,147.75       $1,270.9346   $1,270.93   $1,270.90   $1,270.90