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	$209.28	4.410%	$218.5092	$218.51	$218.50	$218.50
Purchase #2	$120.26	4.621%	$125.8172	$125.82	$125.80	$125.80
Purchase #3	$57.66	6.546%	$61.4344	$61.43	$61.45	$61.40
Purchase #4	$49.52	10.270%	$54.6057	$54.61	$54.60	$54.60
Purchase #5	$113.30	3.774%	$117.5759	$117.58	$117.60	$117.60
Purchase #6	$73.79	13.271%	$83.5827	$83.58	$83.60	$83.60
Purchase #7	$16.76	11.714%	$18.7233	$18.72	$18.70	$18.70
7 purchase totals =	$640.57		$680.2484	$680.25	$680.25	$680.20