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 $231.85   3.671%   $240.3612   $240.36   $240.35   $240.40  
  Purchase #2 $191.43   3.193%   $197.5424   $197.54   $197.55   $197.50  
  Purchase #3 $202.96   6.409%   $215.9677   $215.97   $215.95   $216.00  
  Purchase #4 $32.69   4.649%   $34.2098   $34.21   $34.20   $34.20  
  Purchase #5 $234.53   10.435%   $259.0032   $259.00   $259.00   $259.00  
  Purchase #6 $86.67   6.415%   $92.2299   $92.23   $92.25   $92.20  
  Purchase #7 $215.90   13.716%   $245.5128   $245.51   $245.50   $245.50  
  7 purchase totals = $1,196.03       $1,284.8270   $1,284.82   $1,284.80   $1,284.80