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 $204.41   5.599%   $215.8549   $215.85   $215.85   $215.90  
  Purchase #2 $227.63   6.285%   $241.9365   $241.94   $241.95   $241.90  
  Purchase #3 $50.53   6.641%   $53.8857   $53.89   $53.90   $53.90  
  Purchase #4 $57.63   10.455%   $63.6552   $63.66   $63.65   $63.70  
  Purchase #5 $226.25   4.722%   $236.9335   $236.93   $236.95   $236.90  
  Purchase #6 $65.50   12.698%   $73.8172   $73.82   $73.80   $73.80  
  Purchase #7 $18.71   7.527%   $20.1183   $20.12   $20.10   $20.10  
  7 purchase totals = $850.66       $906.2013   $906.21   $906.20   $906.20