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 $95.36   3.219%   $98.4296   $98.43   $98.45   $98.40  
  Purchase #2 $164.61   8.161%   $178.0438   $178.04   $178.05   $178.00  
  Purchase #3 $240.64   11.774%   $268.973   $268.97   $268.95   $269.00  
  Purchase #4 $9.79   7.590%   $10.5331   $10.53   $10.55   $10.50  
  Purchase #5 $15.46   10.724%   $17.1179   $17.12   $17.10   $17.10  
  Purchase #6 $163.68   7.559%   $176.0526   $176.05   $176.05   $176.10  
  Purchase #7 $151.60   11.700%   $169.3372   $169.34   $169.35   $169.30  
  7 purchase totals = $841.14       $918.4872   $918.48   $918.50   $918.40