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 $123.64   8.124%   $133.6845   $133.68   $133.70   $133.70  
  Purchase #2 $68.85   4.195%   $71.7383   $71.74   $71.75   $71.70  
  Purchase #3 $65.47   6.646%   $69.8211   $69.82   $69.80   $69.80  
  Purchase #4 $247.78   11.507%   $276.292   $276.29   $276.30   $276.30  
  Purchase #5 $86.99   9.239%   $95.027   $95.03   $95.05   $95.00  
  Purchase #6 $131.81   7.257%   $141.3755   $141.38   $141.40   $141.40  
  Purchase #7 $114.43   7.648%   $123.1816   $123.18   $123.20   $123.20  
  7 purchase totals = $838.97       $911.1200   $911.12   $911.20   $911.10