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 $63.50   5.233%   $66.823   $66.82   $66.80   $66.80  
  Purchase #2 $245.71   12.680%   $276.866   $276.87   $276.85   $276.90  
  Purchase #3 $8.66   13.422%   $9.8223   $9.82   $9.80   $9.80  
  Purchase #4 $209.37   10.188%   $230.7006   $230.70   $230.70   $230.70  
  Purchase #5 $213.38   8.408%   $231.321   $231.32   $231.30   $231.30  
  Purchase #6 $121.38   6.651%   $129.453   $129.45   $129.45   $129.50  
  Purchase #7 $5.30   13.737%   $6.0281   $6.03   $6.05   $6.00  
  7 purchase totals = $867.30       $951.0140   $951.01   $950.95   $951.00