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 $51.53   13.269%   $58.3675   $58.37   $58.35   $58.40  
  Purchase #2 $145.94   3.270%   $150.7122   $150.71   $150.70   $150.70  
  Purchase #3 $23.35   3.422%   $24.149   $24.15   $24.15   $24.10  
  Purchase #4 $234.92   10.319%   $259.1614   $259.16   $259.15   $259.20  
  Purchase #5 $62.87   4.827%   $65.9047   $65.90   $65.90   $65.90  
  Purchase #6 $111.69   7.239%   $119.7752   $119.78   $119.80   $119.80  
  Purchase #7 $224.54   5.510%   $236.9122   $236.91   $236.90   $236.90  
  7 purchase totals = $854.84       $914.9822   $914.98   $914.95   $915.00