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	$161.43	13.202%	$182.742	$182.74	$182.75	$182.70
Purchase #2	$111.30	6.728%	$118.7883	$118.79	$118.80	$118.80
Purchase #3	$125.76	5.344%	$132.4806	$132.48	$132.50	$132.50
Purchase #4	$144.77	8.398%	$156.9278	$156.93	$156.95	$156.90
Purchase #5	$211.41	3.391%	$218.5789	$218.58	$218.60	$218.60
Purchase #6	$79.27	13.758%	$90.176	$90.18	$90.20	$90.20
Purchase #7	$78.82	3.372%	$81.4778	$81.48	$81.50	$81.50
7 purchase totals =	$912.76		$981.1714	$981.18	$981.30	$981.20