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 $241.94   8.648%   $262.863   $262.86   $262.85   $262.90  
  Purchase #2 $41.28   11.478%   $46.0181   $46.02   $46.00   $46.00  
  Purchase #3 $90.50   12.411%   $101.732   $101.73   $101.75   $101.70  
  Purchase #4 $215.77   6.424%   $229.6311   $229.63   $229.65   $229.60  
  Purchase #5 $22.86   13.787%   $26.0117   $26.01   $26.00   $26.00  
  Purchase #6 $7.36   12.811%   $8.3029   $8.30   $8.30   $8.30  
  Purchase #7 $48.26   3.213%   $49.8106   $49.81   $49.80   $49.80  
  7 purchase totals = $667.97       $724.3694   $724.36   $724.35   $724.30