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 $66.94   10.617%   $74.047   $74.05   $74.05   $74.00  
  Purchase #2 $244.40   5.843%   $258.6803   $258.68   $258.70   $258.70  
  Purchase #3 $196.64   4.443%   $205.3767   $205.38   $205.40   $205.40  
  Purchase #4 $187.76   8.420%   $203.5694   $203.57   $203.55   $203.60  
  Purchase #5 $75.65   3.778%   $78.5081   $78.51   $78.50   $78.50  
  Purchase #6 $192.83   4.867%   $202.215   $202.22   $202.20   $202.20  
  Purchase #7 $219.95   6.125%   $233.4219   $233.42   $233.40   $233.40  
  7 purchase totals = $1,184.17       $1,255.8184   $1,255.83   $1,255.80   $1,255.80