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 $193.44   7.799%   $208.5264   $208.53   $208.55   $208.50  
  Purchase #2 $12.53   6.113%   $13.296   $13.30   $13.30   $13.30  
  Purchase #3 $149.44   4.636%   $156.368   $156.37   $156.35   $156.40  
  Purchase #4 $195.50   11.844%   $218.655   $218.66   $218.65   $218.70  
  Purchase #5 $217.87   6.229%   $231.4411   $231.44   $231.45   $231.40  
  Purchase #6 $61.73   13.269%   $69.921   $69.92   $69.90   $69.90  
  Purchase #7 $242.34   9.356%   $265.0133   $265.01   $265.00   $265.00  
  7 purchase totals = $1,072.85       $1,163.2208   $1,163.23   $1,163.20   $1,163.20