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	$17.40	12.170%	$19.5176	$19.52	$19.50	$19.50
Purchase #2	$9.78	3.854%	$10.1569	$10.16	$10.15	$10.20
Purchase #3	$90.29	11.198%	$100.4007	$100.40	$100.40	$100.40
Purchase #4	$9.70	7.340%	$10.412	$10.41	$10.40	$10.40
Purchase #5	$9.89	13.104%	$11.186	$11.19	$11.20	$11.20
Purchase #6	$170.83	5.480%	$180.1915	$180.19	$180.20	$180.20
Purchase #7	$165.37	3.759%	$171.5863	$171.59	$171.60	$171.60
7 purchase totals =	$473.26		$503.4510	$503.46	$503.45	$503.50