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	$109.52	11.532%	$122.1498	$122.15	$122.15	$122.10
Purchase #2	$60.88	10.814%	$67.4636	$67.46	$67.45	$67.50
Purchase #3	$141.58	3.540%	$146.5919	$146.59	$146.60	$146.60
Purchase #4	$27.33	8.300%	$29.5984	$29.60	$29.60	$29.60
Purchase #5	$148.70	5.821%	$157.3558	$157.36	$157.35	$157.40
Purchase #6	$246.46	11.727%	$275.3624	$275.36	$275.35	$275.40
Purchase #7	$75.39	4.233%	$78.5813	$78.58	$78.60	$78.60
7 purchase totals =	$809.86		$877.1032	$877.10	$877.10	$877.20