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 $54.30   8.607%   $58.9736   $58.97   $58.95   $59.00  
  Purchase #2 $106.29   10.301%   $117.2389   $117.24   $117.25   $117.20  
  Purchase #3 $51.91   4.519%   $54.2558   $54.26   $54.25   $54.30  
  Purchase #4 $72.77   5.511%   $76.7804   $76.78   $76.80   $76.80  
  Purchase #5 $85.97   4.362%   $89.72   $89.72   $89.70   $89.70  
  Purchase #6 $245.55   4.823%   $257.3929   $257.39   $257.40   $257.40  
  Purchase #7 $135.35   10.379%   $149.398   $149.40   $149.40   $149.40  
  7 purchase totals = $752.14       $803.7596   $803.76   $803.75   $803.80