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 $111.47   7.509%   $119.8403   $119.84   $119.85   $119.80  
  Purchase #2 $218.99   4.752%   $229.3964   $229.40   $229.40   $229.40  
  Purchase #3 $187.84   12.596%   $211.5003   $211.50   $211.50   $211.50  
  Purchase #4 $143.84   11.825%   $160.8491   $160.85   $160.85   $160.80  
  Purchase #5 $158.25   11.220%   $176.0057   $176.01   $176.00   $176.00  
  Purchase #6 $241.76   4.693%   $253.1058   $253.11   $253.10   $253.10  
  Purchase #7 $68.73   11.400%   $76.5652   $76.57   $76.55   $76.60  
  7 purchase totals = $1,130.88       $1,227.2628   $1,227.28   $1,227.25   $1,227.20