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	$35.82	5.468%	$37.7786	$37.78	$37.80	$37.80
Purchase #2	$95.85	9.262%	$104.7276	$104.73	$104.75	$104.70
Purchase #3	$10.35	7.540%	$11.1304	$11.13	$11.15	$11.10
Purchase #4	$67.52	4.357%	$70.4618	$70.46	$70.45	$70.50
Purchase #5	$99.76	11.457%	$111.1895	$111.19	$111.20	$111.20
Purchase #6	$103.74	12.804%	$117.0229	$117.02	$117.00	$117.00
Purchase #7	$173.50	6.295%	$184.4218	$184.42	$184.40	$184.40
7 purchase totals =	$586.54		$636.7326	$636.73	$636.75	$636.70