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 $34.64   11.532%   $38.6347   $38.63   $38.65   $38.60  
  Purchase #2 $245.91   5.119%   $258.4981   $258.50   $258.50   $258.50  
  Purchase #3 $117.53   5.608%   $124.1211   $124.12   $124.10   $124.10  
  Purchase #4 $142.57   9.599%   $156.2553   $156.26   $156.25   $156.30  
  Purchase #5 $69.74   3.202%   $71.9731   $71.97   $71.95   $72.00  
  Purchase #6 $97.78   3.285%   $100.9921   $100.99   $101.00   $101.00  
  Purchase #7 $170.70   3.414%   $176.5277   $176.53   $176.55   $176.50  
  7 purchase totals = $878.87       $927.0021   $927.00   $927.00   $927.00