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 $121.83   4.275%   $127.0382   $127.04   $127.05   $127.00  
  Purchase #2 $58.98   10.632%   $65.2508   $65.25   $65.25   $65.30  
  Purchase #3 $161.36   8.198%   $174.5883   $174.59   $174.60   $174.60  
  Purchase #4 $86.54   9.173%   $94.4783   $94.48   $94.50   $94.50  
  Purchase #5 $46.84   7.564%   $50.383   $50.38   $50.40   $50.40  
  Purchase #6 $235.30   12.205%   $264.0184   $264.02   $264.00   $264.00  
  Purchase #7 $101.93   5.780%   $107.8216   $107.82   $107.80   $107.80  
  7 purchase totals = $812.78       $883.5786   $883.58   $883.60   $883.60