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	$240.96	13.493%	$273.4727	$273.47	$273.45	$273.50
Purchase #2	$28.90	11.680%	$32.2755	$32.28	$32.30	$32.30
Purchase #3	$152.67	6.493%	$162.5829	$162.58	$162.60	$162.60
Purchase #4	$112.82	12.846%	$127.3129	$127.31	$127.30	$127.30
Purchase #5	$152.80	8.723%	$166.1287	$166.13	$166.15	$166.10
Purchase #6	$182.42	9.233%	$199.2628	$199.26	$199.25	$199.30
Purchase #7	$242.64	8.188%	$262.5074	$262.51	$262.50	$262.50
7 purchase totals =	$1,113.21		$1,223.5429	$1,223.54	$1,223.55	$1,223.60