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 $248.41   13.440%   $281.7963   $281.80   $281.80   $281.80  
  Purchase #2 $108.74   4.413%   $113.5387   $113.54   $113.55   $113.50  
  Purchase #3 $15.86   7.534%   $17.0549   $17.05   $17.05   $17.10  
  Purchase #4 $157.54   4.550%   $164.7081   $164.71   $164.70   $164.70  
  Purchase #5 $108.92   3.750%   $113.0045   $113.00   $113.00   $113.00  
  Purchase #6 $194.49   9.827%   $213.6025   $213.60   $213.60   $213.60  
  Purchase #7 $48.73   11.645%   $54.4046   $54.40   $54.40   $54.40  
  7 purchase totals = $882.69       $958.1096   $958.10   $958.10   $958.10