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 $249.46   10.653%   $276.035   $276.04   $276.05   $276.00  
  Purchase #2 $246.34   13.867%   $280.5   $280.50   $280.50   $280.50  
  Purchase #3 $84.45   7.623%   $90.8876   $90.89   $90.90   $90.90  
  Purchase #4 $30.61   13.126%   $34.6279   $34.63   $34.65   $34.60  
  Purchase #5 $135.62   10.364%   $149.6757   $149.68   $149.70   $149.70  
  Purchase #6 $200.71   6.665%   $214.0873   $214.09   $214.10   $214.10  
  Purchase #7 $113.41   8.366%   $122.8979   $122.90   $122.90   $122.90  
  7 purchase totals = $1,060.60       $1,168.7114   $1,168.73   $1,168.80   $1,168.70