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 $182.95   11.136%   $203.3233   $203.32   $203.30   $203.30  
  Purchase #2 $247.67   11.696%   $276.6375   $276.64   $276.65   $276.60  
  Purchase #3 $84.55   8.103%   $91.4011   $91.40   $91.40   $91.40  
  Purchase #4 $221.75   7.599%   $238.6008   $238.60   $238.60   $238.60  
  Purchase #5 $109.53   6.390%   $116.529   $116.53   $116.55   $116.50  
  Purchase #6 $94.94   6.812%   $101.4073   $101.41   $101.40   $101.40  
  Purchase #7 $147.75   3.201%   $152.4795   $152.48   $152.50   $152.50  
  7 purchase totals = $1,089.14       $1,180.3785   $1,180.38   $1,180.40   $1,180.30