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	$51.56	3.701%	$53.4682	$53.47	$53.45	$53.50
Purchase #2	$249.52	6.560%	$265.8885	$265.89	$265.90	$265.90
Purchase #3	$40.78	3.523%	$42.2167	$42.22	$42.20	$42.20
Purchase #4	$104.42	9.586%	$114.4297	$114.43	$114.45	$114.40
Purchase #5	$248.83	12.222%	$279.242	$279.24	$279.25	$279.20
Purchase #6	$19.59	13.596%	$22.2535	$22.25	$22.25	$22.30
Purchase #7	$189.56	7.766%	$204.2812	$204.28	$204.30	$204.30
7 purchase totals =	$904.26		$981.7798	$981.78	$981.80	$981.80