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 $90.35   6.691%   $96.3953   $96.40   $96.40   $96.40  
  Purchase #2 $143.93   4.104%   $149.8369   $149.84   $149.85   $149.80  
  Purchase #3 $106.43   7.207%   $114.1004   $114.10   $114.10   $114.10  
  Purchase #4 $209.82   5.448%   $221.251   $221.25   $221.25   $221.30  
  Purchase #5 $195.49   13.647%   $222.1685   $222.17   $222.15   $222.20  
  Purchase #6 $174.82   8.802%   $190.2077   $190.21   $190.20   $190.20  
  Purchase #7 $32.46   6.863%   $34.6877   $34.69   $34.70   $34.70  
  7 purchase totals = $953.30       $1,028.6475   $1,028.66   $1,028.65   $1,028.70