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	$23.45	8.245%	$25.3835	$25.38	$25.40	$25.40
Purchase #2	$250.94	9.652%	$275.1607	$275.16	$275.15	$275.20
Purchase #3	$100.45	5.650%	$106.1254	$106.13	$106.15	$106.10
Purchase #4	$18.47	10.133%	$20.3416	$20.34	$20.35	$20.30
Purchase #5	$32.68	13.740%	$37.1702	$37.17	$37.15	$37.20
Purchase #6	$52.94	4.631%	$55.3917	$55.39	$55.40	$55.40
Purchase #7	$48.53	3.599%	$50.2766	$50.28	$50.30	$50.30
7 purchase totals =	$527.46		$569.8497	$569.85	$569.90	$569.90