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	$99.90	9.719%	$109.6093	$109.61	$109.60	$109.60
Purchase #2	$126.78	3.548%	$131.2782	$131.28	$131.30	$131.30
Purchase #3	$126.41	3.227%	$130.4893	$130.49	$130.50	$130.50
Purchase #4	$180.72	4.682%	$189.1813	$189.18	$189.20	$189.20
Purchase #5	$46.90	3.393%	$48.4913	$48.49	$48.50	$48.50
Purchase #6	$39.64	11.274%	$44.109	$44.11	$44.10	$44.10
Purchase #7	$128.68	9.682%	$141.1388	$141.14	$141.15	$141.10
7 purchase totals =	$749.03		$794.2972	$794.30	$794.35	$794.30