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 $208.89   8.409%   $226.4556   $226.46   $226.45   $226.50  
  Purchase #2 $134.42   4.189%   $140.0509   $140.05   $140.05   $140.10  
  Purchase #3 $61.84   11.533%   $68.972   $68.97   $68.95   $69.00  
  Purchase #4 $132.77   5.854%   $140.5424   $140.54   $140.55   $140.50  
  Purchase #5 $205.46   5.117%   $215.9734   $215.97   $215.95   $216.00  
  Purchase #6 $170.64   7.759%   $183.88   $183.88   $183.90   $183.90  
  Purchase #7 $75.71   4.416%   $79.0534   $79.05   $79.05   $79.10  
  7 purchase totals = $989.73       $1,054.9277   $1,054.92   $1,054.90   $1,055.10