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 $244.83   11.328%   $272.5643   $272.56   $272.55   $272.60  
  Purchase #2 $168.34   7.332%   $180.6827   $180.68   $180.70   $180.70  
  Purchase #3 $116.27   6.590%   $123.9322   $123.93   $123.95   $123.90  
  Purchase #4 $205.51   5.746%   $217.3186   $217.32   $217.30   $217.30  
  Purchase #5 $158.97   5.267%   $167.3429   $167.34   $167.35   $167.30  
  Purchase #6 $92.95   4.863%   $97.4702   $97.47   $97.45   $97.50  
  Purchase #7 $241.25   6.499%   $256.9288   $256.93   $256.95   $256.90  
  7 purchase totals = $1,228.12       $1,316.2397   $1,316.23   $1,316.25   $1,316.20