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	$77.96	7.163%	$83.5443	$83.54	$83.55	$83.50
Purchase #2	$141.75	11.832%	$158.5219	$158.52	$158.50	$158.50
Purchase #3	$243.87	11.784%	$272.6076	$272.61	$272.60	$272.60
Purchase #4	$73.69	4.289%	$76.8506	$76.85	$76.85	$76.90
Purchase #5	$170.36	5.758%	$180.1693	$180.17	$180.15	$180.20
Purchase #6	$72.96	10.153%	$80.3676	$80.37	$80.35	$80.40
Purchase #7	$190.57	7.301%	$204.4835	$204.48	$204.50	$204.50
7 purchase totals =	$971.16		$1,056.5448	$1,056.54	$1,056.50	$1,056.60