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 $46.73   12.191%   $52.4269   $52.43   $52.45   $52.40  
  Purchase #2 $172.51   13.427%   $195.6729   $195.67   $195.65   $195.70  
  Purchase #3 $229.82   12.340%   $258.1798   $258.18   $258.20   $258.20  
  Purchase #4 $154.53   7.203%   $165.6608   $165.66   $165.65   $165.70  
  Purchase #5 $208.90   4.742%   $218.806   $218.81   $218.80   $218.80  
  Purchase #6 $76.79   10.598%   $84.9282   $84.93   $84.95   $84.90  
  Purchase #7 $52.35   11.787%   $58.5205   $58.52   $58.50   $58.50  
  7 purchase totals = $941.63       $1,034.1951   $1,034.20   $1,034.20   $1,034.20