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 $62.43   9.147%   $68.1405   $68.14   $68.15   $68.10  
  Purchase #2 $133.31   6.624%   $142.1405   $142.14   $142.15   $142.10  
  Purchase #3 $16.89   10.191%   $18.6113   $18.61   $18.60   $18.60  
  Purchase #4 $41.27   12.419%   $46.3953   $46.40   $46.40   $46.40  
  Purchase #5 $247.71   6.356%   $263.4544   $263.45   $263.45   $263.50  
  Purchase #6 $189.31   5.614%   $199.9379   $199.94   $199.95   $199.90  
  Purchase #7 $176.95   3.563%   $183.2547   $183.25   $183.25   $183.30  
  7 purchase totals = $867.87       $921.9346   $921.93   $921.95   $921.90