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	$247.99	11.159%	$275.6632	$275.66	$275.65	$275.70
Purchase #2	$179.85	4.627%	$188.1717	$188.17	$188.15	$188.20
Purchase #3	$87.47	4.730%	$91.6073	$91.61	$91.60	$91.60
Purchase #4	$161.89	13.407%	$183.5946	$183.59	$183.60	$183.60
Purchase #5	$136.75	9.163%	$149.2804	$149.28	$149.30	$149.30
Purchase #6	$188.99	3.855%	$196.2756	$196.28	$196.30	$196.30
Purchase #7	$55.29	3.389%	$57.1638	$57.16	$57.15	$57.20
7 purchase totals =	$1,058.23		$1,141.7566	$1,141.75	$1,141.75	$1,141.90