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	$110.35	12.609%	$124.264	$124.26	$124.25	$124.30
Purchase #2	$159.56	12.860%	$180.0794	$180.08	$180.10	$180.10
Purchase #3	$165.30	4.114%	$172.1004	$172.10	$172.10	$172.10
Purchase #4	$152.56	4.169%	$158.9202	$158.92	$158.90	$158.90
Purchase #5	$221.86	5.306%	$233.6319	$233.63	$233.65	$233.60
Purchase #6	$226.55	6.781%	$241.9124	$241.91	$241.90	$241.90
Purchase #7	$97.30	3.349%	$100.5586	$100.56	$100.55	$100.60
7 purchase totals =	$1,133.48		$1,211.4669	$1,211.46	$1,211.45	$1,211.50