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	$16.65	13.779%	$18.9442	$18.94	$18.95	$18.90
Purchase #2	$244.52	4.815%	$256.2936	$256.29	$256.30	$256.30
Purchase #3	$83.75	7.471%	$90.007	$90.01	$90.00	$90.00
Purchase #4	$242.66	3.297%	$250.6605	$250.66	$250.65	$250.70
Purchase #5	$222.95	3.420%	$230.5749	$230.57	$230.55	$230.60
Purchase #6	$175.56	7.600%	$188.9026	$188.90	$188.90	$188.90
Purchase #7	$168.67	4.187%	$175.7322	$175.73	$175.75	$175.70
7 purchase totals =	$1,154.76		$1,211.1150	$1,211.10	$1,211.10	$1,211.10