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	$217.40	6.618%	$231.7875	$231.79	$231.80	$231.80
Purchase #2	$43.66	4.300%	$45.5374	$45.54	$45.55	$45.50
Purchase #3	$227.45	5.672%	$240.351	$240.35	$240.35	$240.40
Purchase #4	$247.45	10.526%	$273.4966	$273.50	$273.50	$273.50
Purchase #5	$11.48	4.714%	$12.0212	$12.02	$12.00	$12.00
Purchase #6	$96.65	5.103%	$101.582	$101.58	$101.60	$101.60
Purchase #7	$67.30	10.723%	$74.5166	$74.52	$74.50	$74.50
7 purchase totals =	$911.39		$979.2923	$979.30	$979.30	$979.30