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 $79.58   4.624%   $83.2598   $83.26   $83.25   $83.30  
  Purchase #2 $167.98   11.257%   $186.8895   $186.89   $186.90   $186.90  
  Purchase #3 $9.82   13.111%   $11.1075   $11.11   $11.10   $11.10  
  Purchase #4 $160.38   6.381%   $170.6138   $170.61   $170.60   $170.60  
  Purchase #5 $148.63   6.212%   $157.8629   $157.86   $157.85   $157.90  
  Purchase #6 $165.36   6.761%   $176.54   $176.54   $176.55   $176.50  
  Purchase #7 $154.61   3.631%   $160.2239   $160.22   $160.20   $160.20  
  7 purchase totals = $886.36       $946.4974   $946.49   $946.45   $946.50