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 $234.57   9.584%   $257.0512   $257.05   $257.05   $257.10  
  Purchase #2 $209.97   8.155%   $227.0931   $227.09   $227.10   $227.10  
  Purchase #3 $233.44   10.106%   $257.0314   $257.03   $257.05   $257.00  
  Purchase #4 $227.89   11.237%   $253.498   $253.50   $253.50   $253.50  
  Purchase #5 $56.93   10.376%   $62.8371   $62.84   $62.85   $62.80  
  Purchase #6 $117.76   6.439%   $125.3426   $125.34   $125.35   $125.30  
  Purchase #7 $126.68   11.374%   $141.0886   $141.09   $141.10   $141.10  
  7 purchase totals = $1,207.24       $1,323.9420   $1,323.94   $1,324.00   $1,323.90