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	$204.82	10.296%	$225.9083	$225.91	$225.90	$225.90
Purchase #2	$116.91	8.868%	$127.2776	$127.28	$127.30	$127.30
Purchase #3	$223.30	7.404%	$239.8331	$239.83	$239.85	$239.80
Purchase #4	$85.35	10.476%	$94.2913	$94.29	$94.30	$94.30
Purchase #5	$40.39	11.671%	$45.1039	$45.10	$45.10	$45.10
Purchase #6	$105.37	8.243%	$114.0556	$114.06	$114.05	$114.10
Purchase #7	$137.25	9.485%	$150.2682	$150.27	$150.25	$150.30
7 purchase totals =	$913.39		$996.7380	$996.74	$996.75	$996.80