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 $86.65   11.154%   $96.3149   $96.31   $96.30   $96.30  
  Purchase #2 $158.55   9.222%   $173.1715   $173.17   $173.15   $173.20  
  Purchase #3 $209.25   9.605%   $229.3485   $229.35   $229.35   $229.30  
  Purchase #4 $150.51   10.210%   $165.8771   $165.88   $165.90   $165.90  
  Purchase #5 $59.31   5.599%   $62.6308   $62.63   $62.65   $62.60  
  Purchase #6 $44.25   13.469%   $50.21   $50.21   $50.20   $50.20  
  Purchase #7 $132.63   3.365%   $137.093   $137.09   $137.10   $137.10  
  7 purchase totals = $841.15       $914.6458   $914.64   $914.65   $914.60