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	$82.52	9.680%	$90.5079	$90.51	$90.50	$90.50
Purchase #2	$109.64	10.530%	$121.1851	$121.19	$121.20	$121.20
Purchase #3	$88.97	8.420%	$96.4613	$96.46	$96.45	$96.50
Purchase #4	$128.94	11.435%	$143.6843	$143.68	$143.70	$143.70
Purchase #5	$158.45	6.225%	$168.3135	$168.31	$168.30	$168.30
Purchase #6	$209.31	9.690%	$229.5921	$229.59	$229.60	$229.60
Purchase #7	$121.60	6.333%	$129.3009	$129.30	$129.30	$129.30
7 purchase totals =	$899.43		$979.0451	$979.04	$979.05	$979.10