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 $54.89   8.186%   $59.3833   $59.38   $59.40   $59.40  
  Purchase #2 $73.63   13.441%   $83.5266   $83.53   $83.55   $83.50  
  Purchase #3 $249.56   10.670%   $276.1881   $276.19   $276.20   $276.20  
  Purchase #4 $183.75   6.150%   $195.0506   $195.05   $195.05   $195.10  
  Purchase #5 $101.62   8.456%   $110.213   $110.21   $110.20   $110.20  
  Purchase #6 $162.62   12.606%   $183.1199   $183.12   $183.10   $183.10  
  Purchase #7 $189.92   12.533%   $213.7227   $213.72   $213.70   $213.70  
  7 purchase totals = $1,015.99       $1,121.2042   $1,121.20   $1,121.20   $1,121.20