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	$141.67	6.677%	$151.1293	$151.13	$151.15	$151.10
Purchase #2	$173.46	3.826%	$180.0966	$180.10	$180.10	$180.10
Purchase #3	$249.32	3.830%	$258.869	$258.87	$258.85	$258.90
Purchase #4	$47.79	13.643%	$54.31	$54.31	$54.30	$54.30
Purchase #5	$151.76	13.691%	$172.5375	$172.54	$172.55	$172.50
Purchase #6	$74.66	7.343%	$80.1423	$80.14	$80.15	$80.10
Purchase #7	$108.90	13.231%	$123.3086	$123.31	$123.30	$123.30
7 purchase totals =	$947.56		$1,020.3933	$1,020.40	$1,020.40	$1,020.30