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 $238.32   8.782%   $259.2493   $259.25   $259.25   $259.20  
  Purchase #2 $92.48   13.827%   $105.2672   $105.27   $105.25   $105.30  
  Purchase #3 $173.66   9.767%   $190.6214   $190.62   $190.60   $190.60  
  Purchase #4 $131.65   13.616%   $149.5755   $149.58   $149.60   $149.60  
  Purchase #5 $107.66   4.301%   $112.2905   $112.29   $112.30   $112.30  
  Purchase #6 $46.32   7.154%   $49.6337   $49.63   $49.65   $49.60  
  Purchase #7 $230.25   7.691%   $247.9585   $247.96   $247.95   $248.00  
  7 purchase totals = $1,020.34       $1,114.5961   $1,114.60   $1,114.60   $1,114.60