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 $63.77   8.522%   $69.2045   $69.20   $69.20   $69.20  
  Purchase #2 $162.73   3.372%   $168.2173   $168.22   $168.20   $168.20  
  Purchase #3 $203.39   5.708%   $214.9995   $215.00   $215.00   $215.00  
  Purchase #4 $45.99   11.299%   $51.1864   $51.19   $51.20   $51.20  
  Purchase #5 $238.68   7.832%   $257.3734   $257.37   $257.35   $257.40  
  Purchase #6 $109.36   11.624%   $122.072   $122.07   $122.05   $122.10  
  Purchase #7 $8.71   12.322%   $9.7832   $9.78   $9.80   $9.80  
  7 purchase totals = $832.63       $892.8363   $892.83   $892.80   $892.90