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 $64.65   3.210%   $66.7253   $66.73   $66.75   $66.70  
  Purchase #2 $34.36   9.372%   $37.5802   $37.58   $37.60   $37.60  
  Purchase #3 $194.55   7.493%   $209.1276   $209.13   $209.15   $209.10  
  Purchase #4 $59.26   9.307%   $64.7753   $64.78   $64.80   $64.80  
  Purchase #5 $32.55   9.535%   $35.6536   $35.65   $35.65   $35.70  
  Purchase #6 $108.36   10.109%   $119.3141   $119.31   $119.30   $119.30  
  Purchase #7 $158.39   9.378%   $173.2438   $173.24   $173.25   $173.20  
  7 purchase totals = $652.12       $706.4199   $706.42   $706.50   $706.40