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 $82.72   12.381%   $92.9616   $92.96   $92.95   $93.00  
  Purchase #2 $21.33   8.684%   $23.1823   $23.18   $23.20   $23.20  
  Purchase #3 $40.92   8.534%   $44.4121   $44.41   $44.40   $44.40  
  Purchase #4 $72.31   11.621%   $80.7131   $80.71   $80.70   $80.70  
  Purchase #5 $204.87   9.108%   $223.5296   $223.53   $223.55   $223.50  
  Purchase #6 $208.62   13.364%   $236.5   $236.50   $236.50   $236.50  
  Purchase #7 $13.28   13.721%   $15.1021   $15.10   $15.10   $15.10  
  7 purchase totals = $644.05       $716.4008   $716.39   $716.40   $716.40