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	$18.26	9.812%	$20.0517	$20.05	$20.05	$20.10
Purchase #2	$50.36	10.188%	$55.4907	$55.49	$55.50	$55.50
Purchase #3	$207.52	13.494%	$235.5227	$235.52	$235.50	$235.50
Purchase #4	$102.75	8.856%	$111.8495	$111.85	$111.85	$111.80
Purchase #5	$81.76	8.449%	$88.6679	$88.67	$88.65	$88.70
Purchase #6	$26.44	4.204%	$27.5515	$27.55	$27.55	$27.60
Purchase #7	$146.33	13.259%	$165.7319	$165.73	$165.75	$165.70
7 purchase totals =	$633.42		$704.8659	$704.86	$704.85	$704.90