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 $219.59   11.474%   $244.7858   $244.79   $244.80   $244.80  
  Purchase #2 $150.48   10.709%   $166.5949   $166.59   $166.60   $166.60  
  Purchase #3 $179.42   11.612%   $200.2543   $200.25   $200.25   $200.30  
  Purchase #4 $119.70   11.282%   $133.2046   $133.20   $133.20   $133.20  
  Purchase #5 $189.86   8.461%   $205.9241   $205.92   $205.90   $205.90  
  Purchase #6 $240.49   7.851%   $259.3709   $259.37   $259.35   $259.40  
  Purchase #7 $41.68   10.494%   $46.0539   $46.05   $46.05   $46.10  
  7 purchase totals = $1,141.22       $1,256.1885   $1,256.17   $1,256.15   $1,256.30