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 $208.59   12.544%   $234.7555   $234.76   $234.75   $234.80  
  Purchase #2 $164.44   6.383%   $174.9362   $174.94   $174.95   $174.90  
  Purchase #3 $204.83   6.754%   $218.6642   $218.66   $218.65   $218.70  
  Purchase #4 $142.25   6.811%   $151.9386   $151.94   $151.95   $151.90  
  Purchase #5 $148.88   11.681%   $166.2707   $166.27   $166.25   $166.30  
  Purchase #6 $241.30   11.367%   $268.7286   $268.73   $268.75   $268.70  
  Purchase #7 $249.38   4.419%   $260.4001   $260.40   $260.40   $260.40  
  7 purchase totals = $1,359.67       $1,475.6939   $1,475.70   $1,475.70   $1,475.70