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 $51.66   8.869%   $56.2417   $56.24   $56.25   $56.20  
  Purchase #2 $14.98   7.548%   $16.1107   $16.11   $16.10   $16.10  
  Purchase #3 $117.44   6.351%   $124.8986   $124.90   $124.90   $124.90  
  Purchase #4 $55.46   12.289%   $62.2755   $62.28   $62.30   $62.30  
  Purchase #5 $168.93   13.104%   $191.0666   $191.07   $191.05   $191.10  
  Purchase #6 $82.29   11.543%   $91.7887   $91.79   $91.80   $91.80  
  Purchase #7 $61.91   6.636%   $66.0183   $66.02   $66.00   $66.00  
  7 purchase totals = $552.67       $608.4001   $608.41   $608.40   $608.40