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	$35.29	10.293%	$38.9224	$38.92	$38.90	$38.90
Purchase #2	$62.26	10.244%	$68.6379	$68.64	$68.65	$68.60
Purchase #3	$52.54	10.183%	$57.8901	$57.89	$57.90	$57.90
Purchase #4	$231.72	10.173%	$255.2929	$255.29	$255.30	$255.30
Purchase #5	$236.92	9.510%	$259.4511	$259.45	$259.45	$259.50
Purchase #6	$155.87	8.775%	$169.5476	$169.55	$169.55	$169.50
Purchase #7	$165.93	4.365%	$173.1728	$173.17	$173.15	$173.20
7 purchase totals =	$940.53		$1,022.9148	$1,022.91	$1,022.90	$1,022.90