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	$189.71	4.604%	$198.4442	$198.44	$198.45	$198.40
Purchase #2	$249.87	10.366%	$275.7715	$275.77	$275.75	$275.80
Purchase #3	$133.62	9.229%	$145.9518	$145.95	$145.95	$146.00
Purchase #4	$67.60	5.195%	$71.1118	$71.11	$71.10	$71.10
Purchase #5	$132.91	5.288%	$139.9383	$139.94	$139.95	$139.90
Purchase #6	$88.27	10.591%	$97.6187	$97.62	$97.60	$97.60
Purchase #7	$120.46	5.496%	$127.0805	$127.08	$127.10	$127.10
7 purchase totals =	$982.44		$1,055.9168	$1,055.91	$1,055.90	$1,055.90