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 $224.59   11.550%   $250.5301   $250.53   $250.55   $250.50  
  Purchase #2 $161.49   9.449%   $176.7492   $176.75   $176.75   $176.70  
  Purchase #3 $210.69   11.765%   $235.4777   $235.48   $235.50   $235.50  
  Purchase #4 $243.79   9.266%   $266.3796   $266.38   $266.40   $266.40  
  Purchase #5 $22.83   10.857%   $25.3087   $25.31   $25.30   $25.30  
  Purchase #6 $245.54   13.515%   $278.7247   $278.72   $278.70   $278.70  
  Purchase #7 $101.57   11.296%   $113.0433   $113.04   $113.05   $113.00  
  7 purchase totals = $1,210.50       $1,346.2133   $1,346.21   $1,346.25   $1,346.10