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	$198.56	12.700%	$223.7771	$223.78	$223.80	$223.80
Purchase #2	$115.90	6.850%	$123.8392	$123.84	$123.85	$123.80
Purchase #3	$141.45	3.658%	$146.6242	$146.62	$146.60	$146.60
Purchase #4	$125.40	5.344%	$132.1014	$132.10	$132.10	$132.10
Purchase #5	$45.31	13.453%	$51.4056	$51.41	$51.40	$51.40
Purchase #6	$90.78	7.376%	$97.4759	$97.48	$97.50	$97.50
Purchase #7	$105.64	4.621%	$110.5216	$110.52	$110.50	$110.50
7 purchase totals =	$823.04		$885.7450	$885.75	$885.75	$885.70