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	$63.96	11.491%	$71.3096	$71.31	$71.30	$71.30
Purchase #2	$146.81	3.804%	$152.3947	$152.39	$152.40	$152.40
Purchase #3	$75.30	11.111%	$83.6666	$83.67	$83.65	$83.70
Purchase #4	$7.96	13.441%	$9.0299	$9.03	$9.05	$9.00
Purchase #5	$72.42	12.435%	$81.4254	$81.43	$81.45	$81.40
Purchase #6	$165.98	12.136%	$186.1233	$186.12	$186.10	$186.10
Purchase #7	$59.82	3.324%	$61.8084	$61.81	$61.80	$61.80
7 purchase totals =	$592.25		$645.7579	$645.76	$645.75	$645.70