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 $198.64   13.763%   $225.9788   $225.98   $226.00   $226.00  
  Purchase #2 $54.28   11.178%   $60.3474   $60.35   $60.35   $60.30  
  Purchase #3 $79.84   5.298%   $84.0699   $84.07   $84.05   $84.10  
  Purchase #4 $6.45   12.771%   $7.2737   $7.27   $7.25   $7.30  
  Purchase #5 $196.63   5.510%   $207.4643   $207.46   $207.45   $207.50  
  Purchase #6 $213.54   8.561%   $231.8212   $231.82   $231.80   $231.80  
  Purchase #7 $183.56   13.319%   $208.0084   $208.01   $208.00   $208.00  
  7 purchase totals = $932.94       $1,024.9637   $1,024.96   $1,024.90   $1,025.00