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	$103.87	12.762%	$117.1259	$117.13	$117.15	$117.10
Purchase #2	$60.87	7.404%	$65.3768	$65.38	$65.40	$65.40
Purchase #3	$68.39	12.743%	$77.1049	$77.10	$77.10	$77.10
Purchase #4	$178.60	5.777%	$188.9177	$188.92	$188.90	$188.90
Purchase #5	$97.71	13.832%	$111.2252	$111.23	$111.25	$111.20
Purchase #6	$59.67	13.325%	$67.621	$67.62	$67.60	$67.60
Purchase #7	$189.96	4.558%	$198.6184	$198.62	$198.60	$198.60
7 purchase totals =	$759.07		$825.9899	$826.00	$826.00	$825.90