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 $58.61   3.803%   $60.8389   $60.84   $60.85   $60.80  
  Purchase #2 $208.44   12.245%   $233.9635   $233.96   $233.95   $234.00  
  Purchase #3 $127.73   5.659%   $134.9582   $134.96   $134.95   $135.00  
  Purchase #4 $48.77   12.161%   $54.7009   $54.70   $54.70   $54.70  
  Purchase #5 $60.26   6.493%   $64.1727   $64.17   $64.15   $64.20  
  Purchase #6 $118.54   13.332%   $134.3438   $134.34   $134.35   $134.30  
  Purchase #7 $82.90   3.111%   $85.479   $85.48   $85.50   $85.50  
  7 purchase totals = $705.25       $768.4570   $768.45   $768.45   $768.50