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 $236.26   3.151%   $243.7046   $243.70   $243.70   $243.70  
  Purchase #2 $155.79   13.449%   $176.7422   $176.74   $176.75   $176.70  
  Purchase #3 $74.43   9.104%   $81.2061   $81.21   $81.20   $81.20  
  Purchase #4 $196.94   9.864%   $216.3662   $216.37   $216.35   $216.40  
  Purchase #5 $115.63   3.239%   $119.3753   $119.38   $119.40   $119.40  
  Purchase #6 $139.47   8.858%   $151.8243   $151.82   $151.80   $151.80  
  Purchase #7 $56.32   4.619%   $58.9214   $58.92   $58.90   $58.90  
  7 purchase totals = $974.84       $1,048.1401   $1,048.14   $1,048.10   $1,048.10