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 $223.76   6.226%   $237.6913   $237.69   $237.70   $237.70  
  Purchase #2 $85.57   13.177%   $96.8456   $96.85   $96.85   $96.80  
  Purchase #3 $227.48   7.265%   $244.0064   $244.01   $244.00   $244.00  
  Purchase #4 $170.36   12.222%   $191.1814   $191.18   $191.20   $191.20  
  Purchase #5 $245.26   4.804%   $257.0423   $257.04   $257.05   $257.00  
  Purchase #6 $112.34   5.261%   $118.2502   $118.25   $118.25   $118.30  
  Purchase #7 $149.76   12.689%   $168.763   $168.76   $168.75   $168.80  
  7 purchase totals = $1,214.53       $1,313.7802   $1,313.78   $1,313.80   $1,313.80