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	$172.88	3.285%	$178.5591	$178.56	$178.55	$178.60
Purchase #2	$62.72	11.800%	$70.121	$70.12	$70.10	$70.10
Purchase #3	$11.47	7.432%	$12.3225	$12.32	$12.30	$12.30
Purchase #4	$138.89	5.438%	$146.4428	$146.44	$146.45	$146.40
Purchase #5	$139.63	4.856%	$146.4104	$146.41	$146.40	$146.40
Purchase #6	$158.92	8.443%	$172.3376	$172.34	$172.35	$172.30
Purchase #7	$182.99	3.336%	$189.0945	$189.09	$189.10	$189.10
7 purchase totals =	$867.50		$915.2879	$915.28	$915.25	$915.20