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	$250.40	5.839%	$265.0209	$265.02	$265.00	$265.00
Purchase #2	$112.82	13.456%	$128.0011	$128.00	$128.00	$128.00
Purchase #3	$244.79	11.640%	$273.2836	$273.28	$273.30	$273.30
Purchase #4	$211.49	11.853%	$236.5579	$236.56	$236.55	$236.60
Purchase #5	$74.82	11.122%	$83.1415	$83.14	$83.15	$83.10
Purchase #6	$138.72	10.431%	$153.1899	$153.19	$153.20	$153.20
Purchase #7	$127.34	11.194%	$141.5944	$141.59	$141.60	$141.60
7 purchase totals =	$1,160.38		$1,280.7893	$1,280.78	$1,280.80	$1,280.80