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 $207.76   12.137%   $232.9758   $232.98   $233.00   $233.00  
  Purchase #2 $20.89   11.425%   $23.2767   $23.28   $23.30   $23.30  
  Purchase #3 $71.64   6.532%   $76.3195   $76.32   $76.30   $76.30  
  Purchase #4 $162.42   10.759%   $179.8948   $179.89   $179.90   $179.90  
  Purchase #5 $234.54   7.540%   $252.2243   $252.22   $252.20   $252.20  
  Purchase #6 $132.52   6.527%   $141.1696   $141.17   $141.15   $141.20  
  Purchase #7 $48.78   5.632%   $51.5273   $51.53   $51.55   $51.50  
  7 purchase totals = $878.55       $957.3880   $957.39   $957.40   $957.40