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	$99.46	10.840%	$110.2415	$110.24	$110.25	$110.20
Purchase #2	$146.89	13.840%	$167.2196	$167.22	$167.20	$167.20
Purchase #3	$46.77	4.157%	$48.7142	$48.71	$48.70	$48.70
Purchase #4	$106.83	5.556%	$112.7655	$112.77	$112.75	$112.80
Purchase #5	$174.52	3.753%	$181.0697	$181.07	$181.05	$181.10
Purchase #6	$37.77	11.234%	$42.0131	$42.01	$42.00	$42.00
Purchase #7	$142.49	11.845%	$159.3679	$159.37	$159.35	$159.40
7 purchase totals =	$754.73		$821.3915	$821.39	$821.30	$821.40