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	$159.32	12.852%	$179.7958	$179.80	$179.80	$179.80
Purchase #2	$184.85	7.643%	$198.9781	$198.98	$199.00	$199.00
Purchase #3	$49.90	4.765%	$52.2777	$52.28	$52.30	$52.30
Purchase #4	$54.31	13.560%	$61.6744	$61.67	$61.65	$61.70
Purchase #5	$55.64	3.412%	$57.5384	$57.54	$57.55	$57.50
Purchase #6	$92.77	3.259%	$95.7934	$95.79	$95.80	$95.80
Purchase #7	$85.59	4.495%	$89.4373	$89.44	$89.45	$89.40
7 purchase totals =	$682.38		$735.4951	$735.50	$735.55	$735.50