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 $65.54   12.196%   $73.5333   $73.53   $73.55   $73.50  
  Purchase #2 $69.41   9.846%   $76.2441   $76.24   $76.25   $76.20  
  Purchase #3 $55.98   3.600%   $57.9953   $58.00   $58.00   $58.00  
  Purchase #4 $60.52   13.529%   $68.7078   $68.71   $68.70   $68.70  
  Purchase #5 $82.57   13.672%   $93.859   $93.86   $93.85   $93.90  
  Purchase #6 $194.34   12.622%   $218.8696   $218.87   $218.85   $218.90  
  Purchase #7 $58.60   7.154%   $62.7922   $62.79   $62.80   $62.80  
  7 purchase totals = $586.96       $652.0013   $652.00   $652.00   $652.00