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 $203.49   6.118%   $215.9395   $215.94   $215.95   $215.90  
  Purchase #2 $211.77   5.234%   $222.854   $222.85   $222.85   $222.90  
  Purchase #3 $90.41   11.173%   $100.5115   $100.51   $100.50   $100.50  
  Purchase #4 $178.37   12.443%   $200.5646   $200.56   $200.55   $200.60  
  Purchase #5 $184.73   6.648%   $197.0109   $197.01   $197.00   $197.00  
  Purchase #6 $239.90   7.227%   $257.2376   $257.24   $257.25   $257.20  
  Purchase #7 $92.57   6.517%   $98.6028   $98.60   $98.60   $98.60  
  7 purchase totals = $1,201.24       $1,292.7209   $1,292.71   $1,292.70   $1,292.70