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	$110.66	11.629%	$123.5287	$123.53	$123.55	$123.50
Purchase #2	$175.77	5.149%	$184.8204	$184.82	$184.80	$184.80
Purchase #3	$213.72	11.704%	$238.7338	$238.73	$238.75	$238.70
Purchase #4	$141.74	12.284%	$159.1513	$159.15	$159.15	$159.20
Purchase #5	$97.47	13.297%	$110.4306	$110.43	$110.45	$110.40
Purchase #6	$11.84	6.452%	$12.6039	$12.60	$12.60	$12.60
Purchase #7	$38.68	12.332%	$43.45	$43.45	$43.45	$43.50
7 purchase totals =	$789.88		$872.7187	$872.71	$872.75	$872.70