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 $173.30   6.594%   $184.7274   $184.73   $184.75   $184.70  
  Purchase #2 $186.95   6.778%   $199.6215   $199.62   $199.60   $199.60  
  Purchase #3 $60.43   9.543%   $66.1968   $66.20   $66.20   $66.20  
  Purchase #4 $117.65   11.602%   $131.2998   $131.30   $131.30   $131.30  
  Purchase #5 $217.75   4.129%   $226.7409   $226.74   $226.75   $226.70  
  Purchase #6 $221.26   12.412%   $248.7228   $248.72   $248.70   $248.70  
  Purchase #7 $195.38   4.669%   $204.5023   $204.50   $204.50   $204.50  
  7 purchase totals = $1,172.72       $1,261.8115   $1,261.81   $1,261.80   $1,261.70