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 $32.56   6.799%   $34.7738   $34.77   $34.75   $34.80  
  Purchase #2 $228.76   10.485%   $252.7455   $252.75   $252.75   $252.70  
  Purchase #3 $75.74   9.272%   $82.7626   $82.76   $82.75   $82.80  
  Purchase #4 $195.48   12.856%   $220.6109   $220.61   $220.60   $220.60  
  Purchase #5 $108.65   10.383%   $119.9311   $119.93   $119.95   $119.90  
  Purchase #6 $129.48   5.161%   $136.1625   $136.16   $136.15   $136.20  
  Purchase #7 $211.45   7.164%   $226.5983   $226.60   $226.60   $226.60  
  7 purchase totals = $982.12       $1,073.5847   $1,073.58   $1,073.55   $1,073.60