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	$161.31	6.198%	$171.308	$171.31	$171.30	$171.30
Purchase #2	$187.33	4.860%	$196.4342	$196.43	$196.45	$196.40
Purchase #3	$233.28	9.431%	$255.2806	$255.28	$255.30	$255.30
Purchase #4	$150.73	11.828%	$168.5583	$168.56	$168.55	$168.60
Purchase #5	$31.96	12.123%	$35.8345	$35.83	$35.85	$35.80
Purchase #6	$220.26	5.144%	$231.5902	$231.59	$231.60	$231.60
Purchase #7	$203.65	5.853%	$215.5696	$215.57	$215.55	$215.60
7 purchase totals =	$1,188.52		$1,274.5754	$1,274.57	$1,274.60	$1,274.60