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	$44.60	12.647%	$50.2406	$50.24	$50.25	$50.20
Purchase #2	$243.98	5.811%	$258.1577	$258.16	$258.15	$258.20
Purchase #3	$127.27	12.219%	$142.8211	$142.82	$142.80	$142.80
Purchase #4	$151.31	9.548%	$165.7571	$165.76	$165.75	$165.80
Purchase #5	$28.41	9.450%	$31.0947	$31.09	$31.10	$31.10
Purchase #6	$105.84	13.337%	$119.9559	$119.96	$119.95	$120.00
Purchase #7	$218.42	13.618%	$248.1644	$248.16	$248.15	$248.20
7 purchase totals =	$919.83		$1,016.1915	$1,016.19	$1,016.15	$1,016.30