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 $119.85   12.390%   $134.6994   $134.70   $134.70   $134.70  
  Purchase #2 $178.51   4.150%   $185.9182   $185.92   $185.90   $185.90  
  Purchase #3 $42.57   12.296%   $47.8044   $47.80   $47.80   $47.80  
  Purchase #4 $210.39   10.637%   $232.7692   $232.77   $232.75   $232.80  
  Purchase #5 $26.91   12.585%   $30.2966   $30.30   $30.30   $30.30  
  Purchase #6 $104.92   12.622%   $118.163   $118.16   $118.15   $118.20  
  Purchase #7 $75.58   12.854%   $85.2951   $85.30   $85.30   $85.30  
  7 purchase totals = $758.73       $834.9459   $834.95   $834.90   $835.00