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	$101.46	10.685%	$112.301	$112.30	$112.30	$112.30
Purchase #2	$150.96	9.604%	$165.4582	$165.46	$165.45	$165.50
Purchase #3	$154.58	10.189%	$170.3302	$170.33	$170.35	$170.30
Purchase #4	$245.64	12.155%	$275.4975	$275.50	$275.50	$275.50
Purchase #5	$47.31	10.347%	$52.2052	$52.21	$52.20	$52.20
Purchase #6	$158.41	5.786%	$167.5756	$167.58	$167.60	$167.60
Purchase #7	$117.30	8.304%	$127.0406	$127.04	$127.05	$127.00
7 purchase totals =	$975.66		$1,070.4083	$1,070.42	$1,070.45	$1,070.40