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	$151.60	9.364%	$165.7958	$165.80	$165.80	$165.80
Purchase #2	$248.31	11.808%	$277.6304	$277.63	$277.65	$277.60
Purchase #3	$242.62	10.509%	$268.1169	$268.12	$268.10	$268.10
Purchase #4	$117.76	4.677%	$123.2676	$123.27	$123.25	$123.30
Purchase #5	$239.98	6.566%	$255.7371	$255.74	$255.75	$255.70
Purchase #6	$58.82	11.200%	$65.4078	$65.41	$65.40	$65.40
Purchase #7	$91.68	8.609%	$99.5727	$99.57	$99.55	$99.60
7 purchase totals =	$1,150.77		$1,255.5283	$1,255.54	$1,255.50	$1,255.50