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	$43.95	3.534%	$45.5032	$45.50	$45.50	$45.50
Purchase #2	$143.66	11.323%	$159.9266	$159.93	$159.95	$159.90
Purchase #3	$53.50	12.729%	$60.31	$60.31	$60.30	$60.30
Purchase #4	$179.45	3.269%	$185.3162	$185.32	$185.30	$185.30
Purchase #5	$95.83	4.525%	$100.1663	$100.17	$100.15	$100.20
Purchase #6	$71.61	8.366%	$77.6009	$77.60	$77.60	$77.60
Purchase #7	$178.50	5.618%	$188.5281	$188.53	$188.55	$188.50
7 purchase totals =	$766.50		$817.3513	$817.36	$817.35	$817.30