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	$50.84	12.135%	$57.0094	$57.01	$57.00	$57.00
Purchase #2	$148.80	6.743%	$158.8336	$158.83	$158.85	$158.80
Purchase #3	$90.86	9.235%	$99.2509	$99.25	$99.25	$99.30
Purchase #4	$111.89	8.376%	$121.2619	$121.26	$121.25	$121.30
Purchase #5	$141.25	3.683%	$146.4522	$146.45	$146.45	$146.50
Purchase #6	$37.71	13.213%	$42.6926	$42.69	$42.70	$42.70
Purchase #7	$91.71	12.610%	$103.2746	$103.27	$103.25	$103.30
7 purchase totals =	$673.06		$728.7752	$728.76	$728.75	$728.90