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	$243.71	10.168%	$268.4904	$268.49	$268.50	$268.50
Purchase #2	$192.41	3.120%	$198.4132	$198.41	$198.40	$198.40
Purchase #3	$37.84	7.203%	$40.5656	$40.57	$40.55	$40.60
Purchase #4	$151.27	6.280%	$160.7698	$160.77	$160.75	$160.80
Purchase #5	$214.89	7.632%	$231.2904	$231.29	$231.30	$231.30
Purchase #6	$107.32	8.656%	$116.6096	$116.61	$116.60	$116.60
Purchase #7	$37.31	5.370%	$39.3135	$39.31	$39.30	$39.30
7 purchase totals =	$984.75		$1,055.4525	$1,055.45	$1,055.40	$1,055.50