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 $242.98   6.552%   $258.9   $258.90   $258.90   $258.90  
  Purchase #2 $114.46   4.711%   $119.8522   $119.85   $119.85   $119.90  
  Purchase #3 $16.44   4.828%   $17.2337   $17.23   $17.25   $17.20  
  Purchase #4 $44.90   9.456%   $49.1457   $49.15   $49.15   $49.10  
  Purchase #5 $183.72   13.790%   $209.055   $209.06   $209.05   $209.10  
  Purchase #6 $20.53   8.842%   $22.3453   $22.35   $22.35   $22.30  
  Purchase #7 $181.63   13.575%   $206.2863   $206.29   $206.30   $206.30  
  7 purchase totals = $804.66       $882.8182   $882.83   $882.85   $882.80