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	$158.56	8.542%	$172.1042	$172.10	$172.10	$172.10
Purchase #2	$38.45	4.662%	$40.2425	$40.24	$40.25	$40.20
Purchase #3	$85.39	3.188%	$88.1122	$88.11	$88.10	$88.10
Purchase #4	$28.33	13.339%	$32.1089	$32.11	$32.10	$32.10
Purchase #5	$28.98	10.254%	$31.9516	$31.95	$31.95	$32.00
Purchase #6	$246.51	7.487%	$264.9662	$264.97	$264.95	$265.00
Purchase #7	$194.32	10.569%	$214.8577	$214.86	$214.85	$214.90
7 purchase totals =	$780.54		$844.3433	$844.34	$844.30	$844.40