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	$122.40	4.283%	$127.6424	$127.64	$127.65	$127.60
Purchase #2	$200.47	13.428%	$227.3891	$227.39	$227.40	$227.40
Purchase #3	$56.50	13.383%	$64.0614	$64.06	$64.05	$64.10
Purchase #4	$135.50	12.495%	$152.4307	$152.43	$152.45	$152.40
Purchase #5	$78.32	13.445%	$88.8501	$88.85	$88.85	$88.90
Purchase #6	$215.83	9.394%	$236.1051	$236.11	$236.10	$236.10
Purchase #7	$61.69	6.728%	$65.8405	$65.84	$65.85	$65.80
7 purchase totals =	$870.71		$962.3193	$962.32	$962.35	$962.30