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 $224.68   8.273%   $243.2678   $243.27   $243.25   $243.30  
  Purchase #2 $82.87   13.752%   $94.2663   $94.27   $94.25   $94.30  
  Purchase #3 $57.71   8.801%   $62.7891   $62.79   $62.80   $62.80  
  Purchase #4 $69.41   7.361%   $74.5193   $74.52   $74.50   $74.50  
  Purchase #5 $136.37   9.501%   $149.3265   $149.33   $149.35   $149.30  
  Purchase #6 $40.88   13.285%   $46.3109   $46.31   $46.30   $46.30  
  Purchase #7 $232.77   6.484%   $247.8628   $247.86   $247.85   $247.90  
  7 purchase totals = $844.69       $918.3427   $918.35   $918.30   $918.40