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	$170.81	4.642%	$178.739	$178.74	$178.75	$178.70
Purchase #2	$28.29	13.222%	$32.0305	$32.03	$32.05	$32.00
Purchase #3	$6.50	8.430%	$7.048	$7.05	$7.05	$7.00
Purchase #4	$50.49	11.650%	$56.3721	$56.37	$56.35	$56.40
Purchase #5	$194.37	8.248%	$210.4016	$210.40	$210.40	$210.40
Purchase #6	$25.50	9.855%	$28.013	$28.01	$28.00	$28.00
Purchase #7	$112.81	12.592%	$127.015	$127.02	$127.00	$127.00
7 purchase totals =	$588.77		$639.6192	$639.62	$639.60	$639.50