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 $246.34   7.437%   $264.6603   $264.66   $264.65   $264.70  
  Purchase #2 $75.90   10.565%   $83.9188   $83.92   $83.90   $83.90  
  Purchase #3 $156.90   4.340%   $163.7095   $163.71   $163.70   $163.70  
  Purchase #4 $78.37   8.668%   $85.1631   $85.16   $85.15   $85.20  
  Purchase #5 $209.81   7.497%   $225.5395   $225.54   $225.55   $225.50  
  Purchase #6 $113.55   6.174%   $120.5606   $120.56   $120.55   $120.60  
  Purchase #7 $106.74   11.596%   $119.1176   $119.12   $119.10   $119.10  
  7 purchase totals = $987.61       $1,062.6694   $1,062.67   $1,062.60   $1,062.70