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	$217.87	11.745%	$243.4588	$243.46	$243.45	$243.50
Purchase #2	$64.47	9.681%	$70.7113	$70.71	$70.70	$70.70
Purchase #3	$74.91	11.212%	$83.3089	$83.31	$83.30	$83.30
Purchase #4	$128.45	13.244%	$145.4619	$145.46	$145.45	$145.50
Purchase #5	$182.50	3.483%	$188.8565	$188.86	$188.85	$188.90
Purchase #6	$95.25	6.634%	$101.5689	$101.57	$101.55	$101.60
Purchase #7	$77.47	10.501%	$85.6051	$85.61	$85.60	$85.60
7 purchase totals =	$840.92		$918.9714	$918.98	$918.90	$919.10