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 $80.61   8.589%   $87.5336   $87.53   $87.55   $87.50  
  Purchase #2 $173.43   10.333%   $191.3505   $191.35   $191.35   $191.40  
  Purchase #3 $248.87   5.688%   $263.0257   $263.03   $263.05   $263.00  
  Purchase #4 $85.51   13.168%   $96.77   $96.77   $96.75   $96.80  
  Purchase #5 $65.31   13.752%   $74.2914   $74.29   $74.30   $74.30  
  Purchase #6 $30.63   7.646%   $32.972   $32.97   $32.95   $33.00  
  Purchase #7 $45.82   4.753%   $47.9978   $48.00   $48.00   $48.00  
  7 purchase totals = $730.18       $793.9410   $793.94   $793.95   $794.00