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 $195.69   11.279%   $217.7619   $217.76   $217.75   $217.80  
  Purchase #2 $69.47   5.659%   $73.4013   $73.40   $73.40   $73.40  
  Purchase #3 $26.94   12.326%   $30.2606   $30.26   $30.25   $30.30  
  Purchase #4 $244.93   3.133%   $252.6037   $252.60   $252.60   $252.60  
  Purchase #5 $84.48   13.137%   $95.5781   $95.58   $95.60   $95.60  
  Purchase #6 $37.39   6.494%   $39.8181   $39.82   $39.80   $39.80  
  Purchase #7 $47.90   4.385%   $50.0004   $50.00   $50.00   $50.00  
  7 purchase totals = $706.80       $759.4241   $759.42   $759.40   $759.50