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 $84.54   10.626%   $93.5232   $93.52   $93.50   $93.50  
  Purchase #2 $225.43   12.694%   $254.0461   $254.05   $254.05   $254.00  
  Purchase #3 $78.25   12.597%   $88.1072   $88.11   $88.10   $88.10  
  Purchase #4 $34.92   5.344%   $36.7861   $36.79   $36.80   $36.80  
  Purchase #5 $69.29   5.172%   $72.8737   $72.87   $72.85   $72.90  
  Purchase #6 $24.87   5.102%   $26.1389   $26.14   $26.15   $26.10  
  Purchase #7 $145.81   3.796%   $151.3449   $151.34   $151.35   $151.30  
  7 purchase totals = $663.11       $722.8201   $722.82   $722.80   $722.70