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	$173.81	6.723%	$185.4952	$185.50	$185.50	$185.50
Purchase #2	$215.90	13.843%	$245.787	$245.79	$245.80	$245.80
Purchase #3	$123.44	7.198%	$132.3252	$132.33	$132.35	$132.30
Purchase #4	$227.71	12.375%	$255.8891	$255.89	$255.90	$255.90
Purchase #5	$149.31	7.170%	$160.0155	$160.02	$160.00	$160.00
Purchase #6	$205.58	10.243%	$226.6376	$226.64	$226.65	$226.60
Purchase #7	$128.29	13.123%	$145.1255	$145.13	$145.15	$145.10
7 purchase totals =	$1,224.04		$1,351.2751	$1,351.30	$1,351.35	$1,351.20