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	$102.60	12.686%	$115.6158	$115.62	$115.60	$115.60
Purchase #2	$190.37	6.722%	$203.1667	$203.17	$203.15	$203.20
Purchase #3	$129.29	12.624%	$145.6116	$145.61	$145.60	$145.60
Purchase #4	$223.60	13.865%	$254.6021	$254.60	$254.60	$254.60
Purchase #5	$68.63	3.842%	$71.2668	$71.27	$71.25	$71.30
Purchase #6	$95.66	8.777%	$104.0561	$104.06	$104.05	$104.10
Purchase #7	$99.61	5.675%	$105.2629	$105.26	$105.25	$105.30
7 purchase totals =	$909.76		$999.5820	$999.59	$999.50	$999.70