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	$152.81	4.170%	$159.1822	$159.18	$159.20	$159.20
Purchase #2	$15.50	9.823%	$17.0226	$17.02	$17.00	$17.00
Purchase #3	$127.46	9.732%	$139.8644	$139.86	$139.85	$139.90
Purchase #4	$203.44	3.776%	$211.1219	$211.12	$211.10	$211.10
Purchase #5	$128.83	13.743%	$146.5351	$146.54	$146.55	$146.50
Purchase #6	$177.65	4.330%	$185.3422	$185.34	$185.35	$185.30
Purchase #7	$211.38	6.687%	$225.515	$225.52	$225.50	$225.50
7 purchase totals =	$1,017.07		$1,084.5834	$1,084.58	$1,084.55	$1,084.50