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 $59.36   6.143%   $63.0065   $63.01   $63.00   $63.00  
  Purchase #2 $86.51   12.694%   $97.4916   $97.49   $97.50   $97.50  
  Purchase #3 $247.36   4.634%   $258.8227   $258.82   $258.80   $258.80  
  Purchase #4 $120.34   5.130%   $126.5134   $126.51   $126.50   $126.50  
  Purchase #5 $190.49   8.816%   $207.2836   $207.28   $207.30   $207.30  
  Purchase #6 $186.76   3.215%   $192.7643   $192.76   $192.75   $192.80  
  Purchase #7 $242.55   12.138%   $271.9907   $271.99   $272.00   $272.00  
  7 purchase totals = $1,133.37       $1,217.8728   $1,217.86   $1,217.85   $1,217.90