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 $249.66   5.153%   $262.525   $262.53   $262.55   $262.50  
  Purchase #2 $164.84   10.160%   $181.5877   $181.59   $181.60   $181.60  
  Purchase #3 $54.28   9.513%   $59.4437   $59.44   $59.45   $59.40  
  Purchase #4 $224.57   9.429%   $245.7447   $245.74   $245.75   $245.70  
  Purchase #5 $134.41   7.651%   $144.6937   $144.69   $144.70   $144.70  
  Purchase #6 $61.80   8.739%   $67.2007   $67.20   $67.20   $67.20  
  Purchase #7 $44.64   3.126%   $46.0354   $46.04   $46.05   $46.00  
  7 purchase totals = $934.20       $1,007.2309   $1,007.23   $1,007.30   $1,007.10