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	$131.89	3.235%	$136.1566	$136.16	$136.15	$136.20
Purchase #2	$93.28	12.862%	$105.2777	$105.28	$105.30	$105.30
Purchase #3	$41.27	7.114%	$44.2059	$44.21	$44.20	$44.20
Purchase #4	$64.43	10.412%	$71.1385	$71.14	$71.15	$71.10
Purchase #5	$55.88	10.684%	$61.8502	$61.85	$61.85	$61.90
Purchase #6	$34.83	11.273%	$38.7564	$38.76	$38.75	$38.80
Purchase #7	$120.79	4.320%	$126.0081	$126.01	$126.00	$126.00
7 purchase totals =	$542.37		$583.3934	$583.41	$583.40	$583.50