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	$11.41	9.179%	$12.4573	$12.46	$12.45	$12.50
Purchase #2	$218.36	5.471%	$230.3065	$230.31	$230.30	$230.30
Purchase #3	$85.25	5.213%	$89.6941	$89.69	$89.70	$89.70
Purchase #4	$96.82	5.357%	$102.0066	$102.01	$102.00	$102.00
Purchase #5	$19.61	10.838%	$21.7353	$21.74	$21.75	$21.70
Purchase #6	$33.60	3.790%	$34.8734	$34.87	$34.85	$34.90
Purchase #7	$52.42	11.275%	$58.3304	$58.33	$58.35	$58.30
7 purchase totals =	$517.47		$549.4036	$549.41	$549.40	$549.40