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	$86.33	3.491%	$89.3438	$89.34	$89.35	$89.30
Purchase #2	$63.39	12.549%	$71.3448	$71.34	$71.35	$71.30
Purchase #3	$161.51	10.826%	$178.9951	$179.00	$179.00	$179.00
Purchase #4	$71.88	11.441%	$80.1038	$80.10	$80.10	$80.10
Purchase #5	$58.74	5.152%	$61.7663	$61.77	$61.75	$61.80
Purchase #6	$223.32	5.328%	$235.2185	$235.22	$235.20	$235.20
Purchase #7	$129.97	6.472%	$138.3817	$138.38	$138.40	$138.40
7 purchase totals =	$795.14		$855.1540	$855.15	$855.15	$855.10