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 $229.61   10.185%   $252.9958   $253.00   $253.00   $253.00  
  Purchase #2 $216.83   6.795%   $231.5636   $231.56   $231.55   $231.60  
  Purchase #3 $82.29   11.835%   $92.029   $92.03   $92.05   $92.00  
  Purchase #4 $250.70   3.339%   $259.0709   $259.07   $259.05   $259.10  
  Purchase #5 $245.66   8.698%   $267.0275   $267.03   $267.05   $267.00  
  Purchase #6 $213.69   5.392%   $225.2122   $225.21   $225.20   $225.20  
  Purchase #7 $173.55   8.669%   $188.595   $188.60   $188.60   $188.60  
  7 purchase totals = $1,412.33       $1,516.4940   $1,516.50   $1,516.50   $1,516.50