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 $49.82   7.556%   $53.5844   $53.58   $53.60   $53.60  
  Purchase #2 $64.31   8.358%   $69.685   $69.69   $69.70   $69.70  
  Purchase #3 $233.33   10.311%   $257.3887   $257.39   $257.40   $257.40  
  Purchase #4 $183.53   5.627%   $193.8572   $193.86   $193.85   $193.90  
  Purchase #5 $161.85   3.776%   $167.9615   $167.96   $167.95   $168.00  
  Purchase #6 $51.70   12.578%   $58.2028   $58.20   $58.20   $58.20  
  Purchase #7 $12.99   12.476%   $14.6106   $14.61   $14.60   $14.60  
  7 purchase totals = $757.53       $815.2902   $815.29   $815.30   $815.40