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	$139.49	11.228%	$155.1519	$155.15	$155.15	$155.20
Purchase #2	$46.28	4.521%	$48.3723	$48.37	$48.35	$48.40
Purchase #3	$240.28	5.842%	$254.3172	$254.32	$254.30	$254.30
Purchase #4	$33.68	13.801%	$38.3282	$38.33	$38.35	$38.30
Purchase #5	$121.54	4.813%	$127.3897	$127.39	$127.40	$127.40
Purchase #6	$72.82	10.684%	$80.6001	$80.60	$80.60	$80.60
Purchase #7	$220.57	13.345%	$250.0051	$250.01	$250.00	$250.00
7 purchase totals =	$874.66		$954.1645	$954.17	$954.15	$954.20