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 $32.33   10.522%   $35.7318   $35.73   $35.75   $35.70  
  Purchase #2 $245.76   5.389%   $259.004   $259.00   $259.00   $259.00  
  Purchase #3 $126.68   4.850%   $132.824   $132.82   $132.80   $132.80  
  Purchase #4 $83.71   12.619%   $94.2734   $94.27   $94.25   $94.30  
  Purchase #5 $40.87   5.579%   $43.1501   $43.15   $43.15   $43.20  
  Purchase #6 $161.39   9.522%   $176.7576   $176.76   $176.75   $176.80  
  Purchase #7 $147.69   6.490%   $157.2751   $157.28   $157.30   $157.30  
  7 purchase totals = $838.43       $899.0160   $899.01   $899.00   $899.10