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 $96.49   13.577%   $109.5904   $109.59   $109.60   $109.60  
  Purchase #2 $5.92   6.501%   $6.3049   $6.30   $6.30   $6.30  
  Purchase #3 $41.45   5.563%   $43.7559   $43.76   $43.75   $43.80  
  Purchase #4 $173.84   5.266%   $182.9944   $182.99   $183.00   $183.00  
  Purchase #5 $210.89   9.625%   $231.1882   $231.19   $231.20   $231.20  
  Purchase #6 $249.58   4.731%   $261.3876   $261.39   $261.40   $261.40  
  Purchase #7 $210.29   9.455%   $230.1729   $230.17   $230.15   $230.20  
  7 purchase totals = $988.46       $1,065.3943   $1,065.39   $1,065.40   $1,065.50