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	$147.66	3.302%	$152.5357	$152.54	$152.55	$152.50
Purchase #2	$41.67	8.643%	$45.2715	$45.27	$45.25	$45.30
Purchase #3	$91.91	13.326%	$104.1579	$104.16	$104.15	$104.20
Purchase #4	$12.91	12.650%	$14.5431	$14.54	$14.55	$14.50
Purchase #5	$173.58	6.241%	$184.4131	$184.41	$184.40	$184.40
Purchase #6	$53.81	12.630%	$60.6062	$60.61	$60.60	$60.60
Purchase #7	$28.54	12.396%	$32.0778	$32.08	$32.10	$32.10
7 purchase totals =	$550.08		$593.6053	$593.61	$593.60	$593.60