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	$35.53	5.814%	$37.5957	$37.60	$37.60	$37.60
Purchase #2	$146.75	6.398%	$156.1391	$156.14	$156.15	$156.10
Purchase #3	$58.40	11.452%	$65.088	$65.09	$65.10	$65.10
Purchase #4	$42.46	13.265%	$48.0923	$48.09	$48.10	$48.10
Purchase #5	$66.93	6.176%	$71.0636	$71.06	$71.05	$71.10
Purchase #6	$81.93	8.321%	$88.7474	$88.75	$88.75	$88.70
Purchase #7	$238.56	12.401%	$268.1438	$268.14	$268.15	$268.10
7 purchase totals =	$670.56		$734.8699	$734.87	$734.90	$734.80