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	$90.75	10.363%	$100.1544	$100.15	$100.15	$100.20
Purchase #2	$33.33	3.531%	$34.5069	$34.51	$34.50	$34.50
Purchase #3	$177.49	11.244%	$197.447	$197.45	$197.45	$197.40
Purchase #4	$149.33	11.746%	$166.8703	$166.87	$166.85	$166.90
Purchase #5	$47.90	5.142%	$50.363	$50.36	$50.35	$50.40
Purchase #6	$229.66	11.371%	$255.7746	$255.77	$255.75	$255.80
Purchase #7	$224.63	8.279%	$243.2271	$243.23	$243.25	$243.20
7 purchase totals =	$953.09		$1,048.3433	$1,048.34	$1,048.30	$1,048.40