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 $72.79   3.811%   $75.564   $75.56   $75.55   $75.60  
  Purchase #2 $123.84   8.604%   $134.4952   $134.50   $134.50   $134.50  
  Purchase #3 $95.75   4.649%   $100.2014   $100.20   $100.20   $100.20  
  Purchase #4 $195.53   11.211%   $217.4509   $217.45   $217.45   $217.50  
  Purchase #5 $118.94   4.852%   $124.711   $124.71   $124.70   $124.70  
  Purchase #6 $49.95   7.392%   $53.6423   $53.64   $53.65   $53.60  
  Purchase #7 $144.68   11.453%   $161.2502   $161.25   $161.25   $161.30  
  7 purchase totals = $801.48       $867.3150   $867.31   $867.30   $867.40