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	$227.74	5.172%	$239.5187	$239.52	$239.50	$239.50
Purchase #2	$250.75	13.670%	$285.0275	$285.03	$285.05	$285.00
Purchase #3	$129.88	12.544%	$146.1721	$146.17	$146.15	$146.20
Purchase #4	$86.30	3.453%	$89.2799	$89.28	$89.30	$89.30
Purchase #5	$136.78	11.280%	$152.2088	$152.21	$152.20	$152.20
Purchase #6	$83.67	13.236%	$94.7446	$94.74	$94.75	$94.70
Purchase #7	$70.42	5.553%	$74.3304	$74.33	$74.35	$74.30
7 purchase totals =	$985.54		$1,081.2820	$1,081.28	$1,081.30	$1,081.20