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 $191.42   6.852%   $204.5361   $204.54   $204.55   $204.50  
  Purchase #2 $119.53   7.690%   $128.7219   $128.72   $128.70   $128.70  
  Purchase #3 $244.58   12.757%   $275.7811   $275.78   $275.80   $275.80  
  Purchase #4 $96.61   5.583%   $102.0037   $102.00   $102.00   $102.00  
  Purchase #5 $229.94   12.693%   $259.1263   $259.13   $259.15   $259.10  
  Purchase #6 $248.26   11.309%   $276.3357   $276.34   $276.35   $276.30  
  Purchase #7 $12.73   6.322%   $13.5348   $13.53   $13.55   $13.50  
  7 purchase totals = $1,143.07       $1,260.0396   $1,260.04   $1,260.10   $1,259.90