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 $197.25   5.326%   $207.7555   $207.76   $207.75   $207.80  
  Purchase #2 $235.47   6.479%   $250.7261   $250.73   $250.75   $250.70  
  Purchase #3 $87.57   10.214%   $96.5144   $96.51   $96.50   $96.50  
  Purchase #4 $220.48   13.113%   $249.3915   $249.39   $249.40   $249.40  
  Purchase #5 $183.92   7.562%   $197.828   $197.83   $197.85   $197.80  
  Purchase #6 $175.34   9.205%   $191.48   $191.48   $191.50   $191.50  
  Purchase #7 $125.92   8.239%   $136.2945   $136.29   $136.30   $136.30  
  7 purchase totals = $1,225.95       $1,329.9900   $1,329.99   $1,330.05   $1,330.00