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	$156.79	5.592%	$165.5577	$165.56	$165.55	$165.60
Purchase #2	$99.35	13.395%	$112.6579	$112.66	$112.65	$112.70
Purchase #3	$212.54	13.125%	$240.4359	$240.44	$240.45	$240.40
Purchase #4	$179.39	7.118%	$192.159	$192.16	$192.15	$192.20
Purchase #5	$28.87	3.683%	$29.9333	$29.93	$29.95	$29.90
Purchase #6	$86.58	3.742%	$89.8198	$89.82	$89.80	$89.80
Purchase #7	$38.95	12.389%	$43.7755	$43.78	$43.80	$43.80
7 purchase totals =	$802.47		$874.3391	$874.35	$874.35	$874.40