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	$230.32	7.145%	$246.7764	$246.78	$246.80	$246.80
Purchase #2	$154.54	11.342%	$172.0679	$172.07	$172.05	$172.10
Purchase #3	$213.28	7.786%	$229.886	$229.89	$229.90	$229.90
Purchase #4	$80.45	11.753%	$89.9053	$89.91	$89.90	$89.90
Purchase #5	$83.68	8.608%	$90.8832	$90.88	$90.90	$90.90
Purchase #6	$43.91	10.759%	$48.6343	$48.63	$48.65	$48.60
Purchase #7	$213.85	13.580%	$242.8908	$242.89	$242.90	$242.90
7 purchase totals =	$1,020.03		$1,121.0439	$1,121.05	$1,121.10	$1,121.10