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 $108.99   5.273%   $114.737   $114.74   $114.75   $114.70  
  Purchase #2 $109.99   13.699%   $125.0575   $125.06   $125.05   $125.10  
  Purchase #3 $154.81   3.388%   $160.055   $160.06   $160.05   $160.10  
  Purchase #4 $178.84   9.553%   $195.9246   $195.92   $195.90   $195.90  
  Purchase #5 $226.28   12.618%   $254.832   $254.83   $254.85   $254.80  
  Purchase #6 $96.35   5.390%   $101.5433   $101.54   $101.55   $101.50  
  Purchase #7 $119.85   9.870%   $131.6792   $131.68   $131.70   $131.70  
  7 purchase totals = $995.11       $1,083.8286   $1,083.83   $1,083.85   $1,083.80