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 $41.61   12.354%   $46.7505   $46.75   $46.75   $46.80  
  Purchase #2 $107.38   8.131%   $116.1111   $116.11   $116.10   $116.10  
  Purchase #3 $123.25   5.754%   $130.3418   $130.34   $130.35   $130.30  
  Purchase #4 $100.95   9.357%   $110.3959   $110.40   $110.40   $110.40  
  Purchase #5 $58.90   6.578%   $62.7744   $62.77   $62.75   $62.80  
  Purchase #6 $40.91   13.812%   $46.5605   $46.56   $46.55   $46.60  
  Purchase #7 $9.91   4.142%   $10.3205   $10.32   $10.30   $10.30  
  7 purchase totals = $482.91       $523.2547   $523.25   $523.20   $523.30