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 $190.66   6.452%   $202.9614   $202.96   $202.95   $203.00  
  Purchase #2 $118.76   5.674%   $125.4984   $125.50   $125.50   $125.50  
  Purchase #3 $203.80   7.729%   $219.5517   $219.55   $219.55   $219.60  
  Purchase #4 $86.88   13.662%   $98.7495   $98.75   $98.75   $98.70  
  Purchase #5 $114.90   4.110%   $119.6224   $119.62   $119.60   $119.60  
  Purchase #6 $104.93   11.464%   $116.9592   $116.96   $116.95   $117.00  
  Purchase #7 $195.95   11.694%   $218.8644   $218.86   $218.85   $218.90  
  7 purchase totals = $1,015.88       $1,102.2070   $1,102.20   $1,102.15   $1,102.30