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	$79.90	12.239%	$89.679	$89.68	$89.70	$89.70
Purchase #2	$69.59	3.123%	$71.7633	$71.76	$71.75	$71.80
Purchase #3	$48.98	9.452%	$53.6096	$53.61	$53.60	$53.60
Purchase #4	$190.50	11.749%	$212.8818	$212.88	$212.90	$212.90
Purchase #5	$14.30	10.403%	$15.7876	$15.79	$15.80	$15.80
Purchase #6	$32.36	5.494%	$34.1379	$34.14	$34.15	$34.10
Purchase #7	$213.29	10.481%	$235.6449	$235.64	$235.65	$235.60
7 purchase totals =	$648.92		$713.5041	$713.50	$713.55	$713.50