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	$46.49	12.326%	$52.2204	$52.22	$52.20	$52.20
Purchase #2	$233.83	3.835%	$242.7974	$242.80	$242.80	$242.80
Purchase #3	$159.87	12.476%	$179.8154	$179.82	$179.80	$179.80
Purchase #4	$168.45	10.259%	$185.7313	$185.73	$185.75	$185.70
Purchase #5	$97.76	6.176%	$103.7977	$103.80	$103.80	$103.80
Purchase #6	$100.71	9.394%	$110.1707	$110.17	$110.15	$110.20
Purchase #7	$148.73	13.444%	$168.7253	$168.73	$168.75	$168.70
7 purchase totals =	$955.84		$1,043.2582	$1,043.27	$1,043.25	$1,043.20