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	$47.43	5.384%	$49.9836	$49.98	$50.00	$50.00
Purchase #2	$69.62	13.107%	$78.7451	$78.75	$78.75	$78.70
Purchase #3	$62.97	6.873%	$67.2979	$67.30	$67.30	$67.30
Purchase #4	$42.94	7.799%	$46.2889	$46.29	$46.30	$46.30
Purchase #5	$149.59	11.657%	$167.0277	$167.03	$167.05	$167.00
Purchase #6	$110.31	8.257%	$119.4183	$119.42	$119.40	$119.40
Purchase #7	$105.35	5.194%	$110.8219	$110.82	$110.80	$110.80
7 purchase totals =	$588.21		$639.5834	$639.59	$639.60	$639.50