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	$46.90	4.421%	$48.9734	$48.97	$48.95	$49.00
Purchase #2	$220.56	4.239%	$229.9095	$229.91	$229.90	$229.90
Purchase #3	$7.94	11.325%	$8.8392	$8.84	$8.85	$8.80
Purchase #4	$147.27	11.606%	$164.3622	$164.36	$164.35	$164.40
Purchase #5	$219.29	5.275%	$230.8575	$230.86	$230.85	$230.90
Purchase #6	$133.72	10.385%	$147.6068	$147.61	$147.60	$147.60
Purchase #7	$78.90	13.159%	$89.2825	$89.28	$89.30	$89.30
7 purchase totals =	$854.58		$919.8311	$919.83	$919.80	$919.90