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 $89.67   9.177%   $97.899   $97.90   $97.90   $97.90  
  Purchase #2 $195.32   5.637%   $206.3302   $206.33   $206.35   $206.30  
  Purchase #3 $27.73   9.117%   $30.2581   $30.26   $30.25   $30.30  
  Purchase #4 $105.51   4.804%   $110.5787   $110.58   $110.60   $110.60  
  Purchase #5 $63.32   4.321%   $66.0561   $66.06   $66.05   $66.10  
  Purchase #6 $223.78   10.287%   $246.8002   $246.80   $246.80   $246.80  
  Purchase #7 $101.75   13.348%   $115.3316   $115.33   $115.35   $115.30  
  7 purchase totals = $807.08       $873.2539   $873.26   $873.30   $873.30