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 $84.94   8.782%   $92.3994   $92.40   $92.40   $92.40  
  Purchase #2 $238.26   11.422%   $265.4741   $265.47   $265.45   $265.50  
  Purchase #3 $237.29   10.467%   $262.1271   $262.13   $262.15   $262.10  
  Purchase #4 $113.63   4.196%   $118.3979   $118.40   $118.40   $118.40  
  Purchase #5 $209.98   6.245%   $223.0933   $223.09   $223.10   $223.10  
  Purchase #6 $78.79   12.652%   $88.7585   $88.76   $88.75   $88.80  
  Purchase #7 $150.64   9.271%   $164.6058   $164.61   $164.60   $164.60  
  7 purchase totals = $1,113.53       $1,214.8561   $1,214.86   $1,214.85   $1,214.90