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 $204.50   13.595%   $232.3018   $232.30   $232.30   $232.30  
  Purchase #2 $102.85   3.695%   $106.6503   $106.65   $106.65   $106.70  
  Purchase #3 $125.43   12.621%   $141.2605   $141.26   $141.25   $141.30  
  Purchase #4 $91.74   3.824%   $95.2481   $95.25   $95.25   $95.20  
  Purchase #5 $73.78   5.344%   $77.7228   $77.72   $77.70   $77.70  
  Purchase #6 $100.32   12.819%   $113.18   $113.18   $113.20   $113.20  
  Purchase #7 $47.91   6.673%   $51.107   $51.11   $51.10   $51.10  
  7 purchase totals = $746.53       $817.4705   $817.47   $817.45   $817.50