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 $84.78   13.208%   $95.9777   $95.98   $96.00   $96.00  
  Purchase #2 $28.32   5.711%   $29.9374   $29.94   $29.95   $29.90  
  Purchase #3 $52.27   11.421%   $58.2398   $58.24   $58.25   $58.20  
  Purchase #4 $28.28   7.221%   $30.3221   $30.32   $30.30   $30.30  
  Purchase #5 $127.68   4.165%   $132.9979   $133.00   $133.00   $133.00  
  Purchase #6 $244.91   8.383%   $265.4408   $265.44   $265.45   $265.40  
  Purchase #7 $128.88   12.170%   $144.5647   $144.56   $144.55   $144.60  
  7 purchase totals = $695.12       $757.4804   $757.48   $757.50   $757.40