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	$126.41	12.707%	$142.4729	$142.47	$142.45	$142.50
Purchase #2	$161.53	5.819%	$170.9294	$170.93	$170.95	$170.90
Purchase #3	$223.40	12.516%	$251.3607	$251.36	$251.35	$251.40
Purchase #4	$52.38	3.692%	$54.3139	$54.31	$54.30	$54.30
Purchase #5	$105.30	11.846%	$117.7738	$117.77	$117.75	$117.80
Purchase #6	$118.53	7.407%	$127.3095	$127.31	$127.30	$127.30
Purchase #7	$114.27	6.667%	$121.8884	$121.89	$121.90	$121.90
7 purchase totals =	$901.82		$986.0486	$986.04	$986.00	$986.10