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 $227.96   11.791%   $254.8388   $254.84   $254.85   $254.80  
  Purchase #2 $229.44   10.161%   $252.7534   $252.75   $252.75   $252.80  
  Purchase #3 $14.76   13.265%   $16.7179   $16.72   $16.70   $16.70  
  Purchase #4 $214.78   8.430%   $232.886   $232.89   $232.90   $232.90  
  Purchase #5 $96.34   5.740%   $101.8699   $101.87   $101.85   $101.90  
  Purchase #6 $221.91   10.186%   $244.5138   $244.51   $244.50   $244.50  
  Purchase #7 $235.46   6.467%   $250.6872   $250.69   $250.70   $250.70  
  7 purchase totals = $1,240.65       $1,354.2670   $1,354.27   $1,354.25   $1,354.30