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 $204.62   6.178%   $217.2614   $217.26   $217.25   $217.30  
  Purchase #2 $183.92   11.780%   $205.5858   $205.59   $205.60   $205.60  
  Purchase #3 $62.76   6.869%   $67.071   $67.07   $67.05   $67.10  
  Purchase #4 $21.97   11.198%   $24.4302   $24.43   $24.45   $24.40  
  Purchase #5 $235.67   11.135%   $261.9119   $261.91   $261.90   $261.90  
  Purchase #6 $189.68   4.810%   $198.8036   $198.80   $198.80   $198.80  
  Purchase #7 $180.55   3.103%   $186.1525   $186.15   $186.15   $186.20  
  7 purchase totals = $1,079.17       $1,161.2164   $1,161.21   $1,161.20   $1,161.30