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 $227.91   6.448%   $242.6056   $242.61   $242.60   $242.60  
  Purchase #2 $94.27   13.146%   $106.6627   $106.66   $106.65   $106.70  
  Purchase #3 $121.45   8.498%   $131.7708   $131.77   $131.75   $131.80  
  Purchase #4 $187.63   4.128%   $195.3754   $195.38   $195.40   $195.40  
  Purchase #5 $173.30   10.500%   $191.4965   $191.50   $191.50   $191.50  
  Purchase #6 $192.92   7.306%   $207.0147   $207.01   $207.00   $207.00  
  Purchase #7 $18.42   6.316%   $19.5834   $19.58   $19.60   $19.60  
  7 purchase totals = $1,015.90       $1,094.5091   $1,094.51   $1,094.50   $1,094.60