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 $151.95   10.583%   $168.0309   $168.03   $168.05   $168.00  
  Purchase #2 $123.71   4.185%   $128.8873   $128.89   $128.90   $128.90  
  Purchase #3 $229.88   7.724%   $247.6359   $247.64   $247.65   $247.60  
  Purchase #4 $34.96   11.867%   $39.1087   $39.11   $39.10   $39.10  
  Purchase #5 $61.85   11.588%   $69.0172   $69.02   $69.00   $69.00  
  Purchase #6 $24.43   4.387%   $25.5017   $25.50   $25.50   $25.50  
  Purchase #7 $215.77   8.132%   $233.3164   $233.32   $233.30   $233.30  
  7 purchase totals = $842.55       $911.4981   $911.51   $911.50   $911.40