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	$147.55	11.826%	$164.9993	$165.00	$165.00	$165.00
Purchase #2	$143.72	8.742%	$156.284	$156.28	$156.30	$156.30
Purchase #3	$155.78	6.529%	$165.9509	$165.95	$165.95	$166.00
Purchase #4	$157.73	6.659%	$168.2332	$168.23	$168.25	$168.20
Purchase #5	$108.82	13.259%	$123.2484	$123.25	$123.25	$123.20
Purchase #6	$17.65	8.624%	$19.1721	$19.17	$19.15	$19.20
Purchase #7	$134.62	4.431%	$140.585	$140.59	$140.60	$140.60
7 purchase totals =	$865.87		$938.4729	$938.47	$938.50	$938.50