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 $67.53   12.452%   $75.9388   $75.94   $75.95   $75.90  
  Purchase #2 $46.39   4.430%   $48.4451   $48.45   $48.45   $48.40  
  Purchase #3 $107.90   10.629%   $119.3687   $119.37   $119.35   $119.40  
  Purchase #4 $25.93   7.381%   $27.8439   $27.84   $27.85   $27.80  
  Purchase #5 $243.61   13.451%   $276.378   $276.38   $276.40   $276.40  
  Purchase #6 $131.92   9.432%   $144.3627   $144.36   $144.35   $144.40  
  Purchase #7 $122.67   12.817%   $138.3926   $138.39   $138.40   $138.40  
  7 purchase totals = $745.95       $830.7298   $830.73   $830.75   $830.70