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 $60.38   12.422%   $67.8804   $67.88   $67.90   $67.90  
  Purchase #2 $71.46   6.386%   $76.0234   $76.02   $76.00   $76.00  
  Purchase #3 $211.64   8.278%   $229.1596   $229.16   $229.15   $229.20  
  Purchase #4 $62.31   5.355%   $65.6467   $65.65   $65.65   $65.60  
  Purchase #5 $179.87   10.742%   $199.1916   $199.19   $199.20   $199.20  
  Purchase #6 $60.98   6.779%   $65.1138   $65.11   $65.10   $65.10  
  Purchase #7 $103.63   9.354%   $113.3236   $113.32   $113.30   $113.30  
  7 purchase totals = $750.27       $816.3391   $816.33   $816.30   $816.30