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 $152.46   7.561%   $163.9875   $163.99   $164.00   $164.00  
  Purchase #2 $89.67   13.385%   $101.6723   $101.67   $101.65   $101.70  
  Purchase #3 $28.49   5.142%   $29.955   $29.96   $29.95   $30.00  
  Purchase #4 $95.99   9.700%   $105.301   $105.30   $105.30   $105.30  
  Purchase #5 $151.65   4.422%   $158.356   $158.36   $158.35   $158.40  
  Purchase #6 $182.35   9.382%   $199.4581   $199.46   $199.45   $199.50  
  Purchase #7 $98.82   3.680%   $102.4566   $102.46   $102.45   $102.50  
  7 purchase totals = $799.43       $861.1865   $861.20   $861.15   $861.40