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	$25.37	11.113%	$28.1894	$28.19	$28.20	$28.20
Purchase #2	$109.96	12.846%	$124.0855	$124.09	$124.10	$124.10
Purchase #3	$149.65	4.705%	$156.691	$156.69	$156.70	$156.70
Purchase #4	$64.33	13.296%	$72.8833	$72.88	$72.90	$72.90
Purchase #5	$84.63	6.862%	$90.4373	$90.44	$90.45	$90.40
Purchase #6	$169.64	9.603%	$185.9305	$185.93	$185.95	$185.90
Purchase #7	$105.65	5.198%	$111.1417	$111.14	$111.15	$111.10
7 purchase totals =	$709.23		$769.3587	$769.36	$769.45	$769.30