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	$18.48	8.663%	$20.0809	$20.08	$20.10	$20.10
Purchase #2	$99.95	3.692%	$103.6402	$103.64	$103.65	$103.60
Purchase #3	$23.85	5.120%	$25.0711	$25.07	$25.05	$25.10
Purchase #4	$94.75	12.397%	$106.4962	$106.50	$106.50	$106.50
Purchase #5	$18.41	11.263%	$20.4835	$20.48	$20.50	$20.50
Purchase #6	$141.47	3.543%	$146.4823	$146.48	$146.50	$146.50
Purchase #7	$75.76	13.858%	$86.2588	$86.26	$86.25	$86.30
7 purchase totals =	$472.67		$508.5130	$508.51	$508.55	$508.60