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 $224.44   13.383%   $254.4768   $254.48   $254.50   $254.50  
  Purchase #2 $227.98   13.575%   $258.9283   $258.93   $258.95   $258.90  
  Purchase #3 $244.70   3.280%   $252.7262   $252.73   $252.75   $252.70  
  Purchase #4 $91.86   6.236%   $97.5884   $97.59   $97.60   $97.60  
  Purchase #5 $101.61   5.830%   $107.5339   $107.53   $107.55   $107.50  
  Purchase #6 $137.70   13.284%   $155.9921   $155.99   $156.00   $156.00  
  Purchase #7 $94.40   5.643%   $99.727   $99.73   $99.75   $99.70  
  7 purchase totals = $1,122.69       $1,226.9727   $1,226.98   $1,227.10   $1,226.90