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 $243.59   3.269%   $251.553   $251.55   $251.55   $251.60  
  Purchase #2 $51.32   13.303%   $58.1471   $58.15   $58.15   $58.10  
  Purchase #3 $173.34   7.450%   $186.2538   $186.25   $186.25   $186.30  
  Purchase #4 $69.97   6.517%   $74.5299   $74.53   $74.55   $74.50  
  Purchase #5 $244.56   8.345%   $264.9685   $264.97   $264.95   $265.00  
  Purchase #6 $148.71   6.341%   $158.1397   $158.14   $158.15   $158.10  
  Purchase #7 $223.32   11.188%   $248.305   $248.31   $248.30   $248.30  
  7 purchase totals = $1,154.81       $1,241.8970   $1,241.90   $1,241.90   $1,241.90