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 $61.76   10.654%   $68.3399   $68.34   $68.35   $68.30  
  Purchase #2 $18.53   4.635%   $19.3889   $19.39   $19.40   $19.40  
  Purchase #3 $6.67   13.331%   $7.5592   $7.56   $7.55   $7.60  
  Purchase #4 $47.55   12.496%   $53.4918   $53.49   $53.50   $53.50  
  Purchase #5 $159.53   12.422%   $179.3468   $179.35   $179.35   $179.30  
  Purchase #6 $15.90   13.442%   $18.0373   $18.04   $18.05   $18.00  
  Purchase #7 $144.36   4.628%   $151.041   $151.04   $151.05   $151.00  
  7 purchase totals = $454.30       $497.2049   $497.21   $497.25   $497.10