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 $67.98   11.131%   $75.5469   $75.55   $75.55   $75.50  
  Purchase #2 $213.80   13.841%   $243.3921   $243.39   $243.40   $243.40  
  Purchase #3 $46.25   3.794%   $48.0047   $48.00   $48.00   $48.00  
  Purchase #4 $239.91   8.535%   $260.3863   $260.39   $260.40   $260.40  
  Purchase #5 $82.67   12.378%   $92.9029   $92.90   $92.90   $92.90  
  Purchase #6 $84.47   10.249%   $93.1273   $93.13   $93.15   $93.10  
  Purchase #7 $145.77   6.391%   $155.0862   $155.09   $155.10   $155.10  
  7 purchase totals = $880.85       $968.4464   $968.45   $968.50   $968.40