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	$243.66	13.192%	$275.8036	$275.80	$275.80	$275.80
Purchase #2	$26.85	5.474%	$28.3198	$28.32	$28.30	$28.30
Purchase #3	$13.44	13.801%	$15.2949	$15.29	$15.30	$15.30
Purchase #4	$59.86	11.493%	$66.7397	$66.74	$66.75	$66.70
Purchase #5	$249.30	8.147%	$269.6105	$269.61	$269.60	$269.60
Purchase #6	$50.84	6.326%	$54.0561	$54.06	$54.05	$54.10
Purchase #7	$212.56	8.628%	$230.8997	$230.90	$230.90	$230.90
7 purchase totals =	$856.51		$940.7243	$940.72	$940.70	$940.70