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 $62.70   8.673%   $68.138   $68.14   $68.15   $68.10  
  Purchase #2 $232.51   9.232%   $253.9753   $253.98   $254.00   $254.00  
  Purchase #3 $22.78   9.147%   $24.8637   $24.86   $24.85   $24.90  
  Purchase #4 $83.68   6.863%   $89.423   $89.42   $89.40   $89.40  
  Purchase #5 $36.25   4.601%   $37.9179   $37.92   $37.90   $37.90  
  Purchase #6 $159.53   8.289%   $172.7534   $172.75   $172.75   $172.80  
  Purchase #7 $211.66   4.717%   $221.644   $221.64   $221.65   $221.60  
  7 purchase totals = $809.11       $868.7153   $868.71   $868.70   $868.70