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 $212.31   5.768%   $224.556   $224.56   $224.55   $224.60  
  Purchase #2 $23.53   13.609%   $26.7322   $26.73   $26.75   $26.70  
  Purchase #3 $249.97   7.719%   $269.2652   $269.27   $269.25   $269.30  
  Purchase #4 $205.46   12.523%   $231.1898   $231.19   $231.20   $231.20  
  Purchase #5 $94.86   5.718%   $100.2841   $100.28   $100.30   $100.30  
  Purchase #6 $44.56   9.518%   $48.8012   $48.80   $48.80   $48.80  
  Purchase #7 $59.29   4.809%   $62.1413   $62.14   $62.15   $62.10  
  7 purchase totals = $889.98       $962.9698   $962.97   $963.00   $963.00