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	$115.36	13.144%	$130.5229	$130.52	$130.50	$130.50
Purchase #2	$87.89	7.690%	$94.6487	$94.65	$94.65	$94.60
Purchase #3	$129.62	9.852%	$142.3902	$142.39	$142.40	$142.40
Purchase #4	$82.33	4.221%	$85.8051	$85.81	$85.80	$85.80
Purchase #5	$226.73	13.741%	$257.885	$257.89	$257.90	$257.90
Purchase #6	$130.79	13.354%	$148.2557	$148.26	$148.25	$148.30
Purchase #7	$29.32	11.130%	$32.5833	$32.58	$32.60	$32.60
7 purchase totals =	$802.04		$892.0909	$892.10	$892.10	$892.10