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 $73.42   4.516%   $76.7356   $76.74   $76.75   $76.70  
  Purchase #2 $193.25   9.413%   $211.4406   $211.44   $211.45   $211.40  
  Purchase #3 $13.32   4.544%   $13.9253   $13.93   $13.95   $13.90  
  Purchase #4 $129.82   4.383%   $135.51   $135.51   $135.50   $135.50  
  Purchase #5 $157.70   5.617%   $166.558   $166.56   $166.55   $166.60  
  Purchase #6 $43.91   10.272%   $48.4204   $48.42   $48.40   $48.40  
  Purchase #7 $232.86   10.369%   $257.0053   $257.01   $257.00   $257.00  
  7 purchase totals = $844.28       $909.5952   $909.61   $909.60   $909.50