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 $236.50   13.613%   $268.6947   $268.69   $268.70   $268.70  
  Purchase #2 $104.81   5.568%   $110.6458   $110.65   $110.65   $110.60  
  Purchase #3 $151.99   4.549%   $158.904   $158.90   $158.90   $158.90  
  Purchase #4 $194.68   5.482%   $205.3524   $205.35   $205.35   $205.40  
  Purchase #5 $153.51   10.159%   $169.1051   $169.11   $169.10   $169.10  
  Purchase #6 $165.91   13.846%   $188.8819   $188.88   $188.90   $188.90  
  Purchase #7 $136.97   4.836%   $143.5939   $143.59   $143.60   $143.60  
  7 purchase totals = $1,144.37       $1,245.1778   $1,245.17   $1,245.20   $1,245.20