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	$17.32	8.694%	$18.8258	$18.83	$18.85	$18.80
Purchase #2	$96.75	13.181%	$109.5026	$109.50	$109.50	$109.50
Purchase #3	$156.60	3.276%	$161.7302	$161.73	$161.75	$161.70
Purchase #4	$43.32	5.775%	$45.8217	$45.82	$45.80	$45.80
Purchase #5	$70.31	11.859%	$78.6481	$78.65	$78.65	$78.60
Purchase #6	$206.35	9.784%	$226.5393	$226.54	$226.55	$226.50
Purchase #7	$155.28	4.688%	$162.5595	$162.56	$162.55	$162.60
7 purchase totals =	$745.93		$803.6272	$803.63	$803.65	$803.50