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 $109.62   8.274%   $118.69   $118.69   $118.70   $118.70  
  Purchase #2 $123.98   7.554%   $133.3454   $133.35   $133.35   $133.30  
  Purchase #3 $121.64   8.824%   $132.3735   $132.37   $132.35   $132.40  
  Purchase #4 $46.99   4.795%   $49.2432   $49.24   $49.25   $49.20  
  Purchase #5 $6.34   10.637%   $7.0144   $7.01   $7.00   $7.00  
  Purchase #6 $227.55   7.581%   $244.8006   $244.80   $244.80   $244.80  
  Purchase #7 $229.74   12.262%   $257.9107   $257.91   $257.90   $257.90  
  7 purchase totals = $865.86       $943.3778   $943.37   $943.35   $943.30