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	$105.68	5.304%	$111.2853	$111.29	$111.30	$111.30
Purchase #2	$129.43	11.865%	$144.7869	$144.79	$144.80	$144.80
Purchase #3	$75.96	6.300%	$80.7455	$80.75	$80.75	$80.70
Purchase #4	$120.64	4.213%	$125.7226	$125.72	$125.70	$125.70
Purchase #5	$96.51	11.679%	$107.7814	$107.78	$107.80	$107.80
Purchase #6	$78.85	4.163%	$82.1325	$82.13	$82.15	$82.10
Purchase #7	$128.40	3.139%	$132.4305	$132.43	$132.45	$132.40
7 purchase totals =	$735.47		$784.8847	$784.89	$784.95	$784.80