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	$240.41	3.424%	$248.6416	$248.64	$248.65	$248.60
Purchase #2	$121.65	12.476%	$136.8271	$136.83	$136.85	$136.80
Purchase #3	$152.52	8.567%	$165.5864	$165.59	$165.60	$165.60
Purchase #4	$183.88	10.651%	$203.4651	$203.47	$203.45	$203.50
Purchase #5	$151.78	13.590%	$172.4069	$172.41	$172.40	$172.40
Purchase #6	$30.52	13.856%	$34.7489	$34.75	$34.75	$34.70
Purchase #7	$179.79	11.481%	$200.4317	$200.43	$200.45	$200.40
7 purchase totals =	$1,060.55		$1,162.1077	$1,162.12	$1,162.15	$1,162.00