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	$109.30	10.204%	$120.453	$120.45	$120.45	$120.50
Purchase #2	$65.99	6.655%	$70.3816	$70.38	$70.40	$70.40
Purchase #3	$156.91	10.109%	$172.772	$172.77	$172.75	$172.80
Purchase #4	$84.76	6.322%	$90.1185	$90.12	$90.10	$90.10
Purchase #5	$91.52	10.135%	$100.7956	$100.80	$100.80	$100.80
Purchase #6	$243.58	4.772%	$255.2036	$255.20	$255.20	$255.20
Purchase #7	$21.46	3.394%	$22.1884	$22.19	$22.20	$22.20
7 purchase totals =	$773.52		$831.9127	$831.91	$831.90	$832.00