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 $69.71   9.261%   $76.1658   $76.17   $76.15   $76.20  
  Purchase #2 $214.59   12.565%   $241.5532   $241.55   $241.55   $241.60  
  Purchase #3 $180.56   8.541%   $195.9816   $195.98   $196.00   $196.00  
  Purchase #4 $45.62   7.330%   $48.9639   $48.96   $48.95   $49.00  
  Purchase #5 $78.98   5.703%   $83.4842   $83.48   $83.50   $83.50  
  Purchase #6 $34.53   9.455%   $37.7948   $37.79   $37.80   $37.80  
  Purchase #7 $192.71   11.247%   $214.3841   $214.38   $214.40   $214.40  
  7 purchase totals = $816.70       $898.3276   $898.31   $898.35   $898.50