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 $98.98   3.158%   $102.1058   $102.11   $102.10   $102.10  
  Purchase #2 $104.84   10.866%   $116.2319   $116.23   $116.25   $116.20  
  Purchase #3 $13.97   7.451%   $15.0109   $15.01   $15.00   $15.00  
  Purchase #4 $160.34   12.747%   $180.7785   $180.78   $180.80   $180.80  
  Purchase #5 $171.85   9.748%   $188.6019   $188.60   $188.60   $188.60  
  Purchase #6 $241.86   8.576%   $262.6019   $262.60   $262.60   $262.60  
  Purchase #7 $83.41   12.724%   $94.0231   $94.02   $94.00   $94.00  
  7 purchase totals = $875.25       $959.3540   $959.35   $959.35   $959.30