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 $56.49   12.557%   $63.5834   $63.58   $63.60   $63.60  
  Purchase #2 $140.69   12.453%   $158.2101   $158.21   $158.20   $158.20  
  Purchase #3 $139.51   10.606%   $154.3064   $154.31   $154.30   $154.30  
  Purchase #4 $56.82   3.277%   $58.682   $58.68   $58.70   $58.70  
  Purchase #5 $227.25   9.119%   $247.9729   $247.97   $247.95   $248.00  
  Purchase #6 $20.98   11.373%   $23.3661   $23.37   $23.35   $23.40  
  Purchase #7 $209.56   11.826%   $234.3426   $234.34   $234.35   $234.30  
  7 purchase totals = $851.30       $940.4635   $940.46   $940.45   $940.50