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 $68.33   12.221%   $76.6806   $76.68   $76.70   $76.70  
  Purchase #2 $206.78   8.458%   $224.2695   $224.27   $224.25   $224.30  
  Purchase #3 $155.99   7.863%   $168.2555   $168.26   $168.25   $168.30  
  Purchase #4 $12.95   4.841%   $13.5769   $13.58   $13.60   $13.60  
  Purchase #5 $149.49   11.368%   $166.484   $166.48   $166.50   $166.50  
  Purchase #6 $42.86   7.264%   $45.9734   $45.97   $45.95   $46.00  
  Purchase #7 $231.49   6.731%   $247.0716   $247.07   $247.05   $247.10  
  7 purchase totals = $867.89       $942.3115   $942.31   $942.30   $942.50