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	$161.46	10.609%	$178.5893	$178.59	$178.60	$178.60
Purchase #2	$114.79	11.362%	$127.8324	$127.83	$127.85	$127.80
Purchase #3	$172.97	13.765%	$196.7793	$196.78	$196.80	$196.80
Purchase #4	$39.52	3.374%	$40.8534	$40.85	$40.85	$40.90
Purchase #5	$8.58	6.203%	$9.1122	$9.11	$9.10	$9.10
Purchase #6	$130.89	4.220%	$136.4136	$136.41	$136.40	$136.40
Purchase #7	$105.41	13.692%	$119.8427	$119.84	$119.85	$119.80
7 purchase totals =	$733.62		$809.4229	$809.41	$809.45	$809.40