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 $52.90   7.328%   $56.7765   $56.78   $56.80   $56.80  
  Purchase #2 $183.25   6.569%   $195.2877   $195.29   $195.30   $195.30  
  Purchase #3 $232.27   12.598%   $261.5314   $261.53   $261.55   $261.50  
  Purchase #4 $70.66   4.117%   $73.5691   $73.57   $73.55   $73.60  
  Purchase #5 $203.42   13.662%   $231.2112   $231.21   $231.20   $231.20  
  Purchase #6 $183.79   12.397%   $206.5744   $206.57   $206.55   $206.60  
  Purchase #7 $161.83   5.605%   $170.9006   $170.90   $170.90   $170.90  
  7 purchase totals = $1,088.12       $1,195.8509   $1,195.85   $1,195.85   $1,195.90