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 $62.54   6.782%   $66.7815   $66.78   $66.80   $66.80  
  Purchase #2 $213.87   10.334%   $235.9713   $235.97   $235.95   $236.00  
  Purchase #3 $99.85   7.195%   $107.0342   $107.03   $107.05   $107.00  
  Purchase #4 $152.39   4.614%   $159.4213   $159.42   $159.40   $159.40  
  Purchase #5 $104.74   10.427%   $115.6612   $115.66   $115.65   $115.70  
  Purchase #6 $211.55   4.564%   $221.2051   $221.21   $221.20   $221.20  
  Purchase #7 $44.58   12.393%   $50.1048   $50.10   $50.10   $50.10  
  7 purchase totals = $889.52       $956.1794   $956.17   $956.15   $956.20