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 $89.87   6.227%   $95.4662   $95.47   $95.45   $95.50  
  Purchase #2 $30.25   9.829%   $33.2233   $33.22   $33.20   $33.20  
  Purchase #3 $180.74   9.443%   $197.8073   $197.81   $197.80   $197.80  
  Purchase #4 $19.30   11.253%   $21.4718   $21.47   $21.45   $21.50  
  Purchase #5 $195.81   10.392%   $216.1586   $216.16   $216.15   $216.20  
  Purchase #6 $41.90   13.284%   $47.466   $47.47   $47.45   $47.50  
  Purchase #7 $202.71   5.243%   $213.3381   $213.34   $213.35   $213.30  
  7 purchase totals = $760.58       $824.9313   $824.94   $824.85   $825.00