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	$70.45	3.513%	$72.9249	$72.92	$72.90	$72.90
Purchase #2	$116.75	7.130%	$125.0743	$125.07	$125.05	$125.10
Purchase #3	$37.66	9.677%	$41.3044	$41.30	$41.30	$41.30
Purchase #4	$48.65	11.684%	$54.3343	$54.33	$54.35	$54.30
Purchase #5	$154.55	12.304%	$173.5658	$173.57	$173.55	$173.60
Purchase #6	$233.66	9.207%	$255.1731	$255.17	$255.15	$255.20
Purchase #7	$240.56	4.212%	$250.6924	$250.69	$250.70	$250.70
7 purchase totals =	$902.28		$973.0692	$973.05	$973.00	$973.10