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 $78.84   12.276%   $88.5184   $88.52   $88.50   $88.50  
  Purchase #2 $240.94   10.265%   $265.6725   $265.67   $265.65   $265.70  
  Purchase #3 $144.41   7.327%   $154.9909   $154.99   $155.00   $155.00  
  Purchase #4 $62.52   10.244%   $68.9245   $68.92   $68.90   $68.90  
  Purchase #5 $151.95   6.676%   $162.0942   $162.09   $162.10   $162.10  
  Purchase #6 $94.46   11.616%   $105.4325   $105.43   $105.45   $105.40  
  Purchase #7 $238.37   12.406%   $267.9422   $267.94   $267.95   $267.90  
  7 purchase totals = $1,011.49       $1,113.5752   $1,113.56   $1,113.55   $1,113.50