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	$106.95	4.364%	$111.6173	$111.62	$111.60	$111.60
Purchase #2	$140.88	10.149%	$155.1779	$155.18	$155.20	$155.20
Purchase #3	$84.51	7.545%	$90.8863	$90.89	$90.90	$90.90
Purchase #4	$205.83	13.257%	$233.1169	$233.12	$233.10	$233.10
Purchase #5	$5.47	6.399%	$5.82	$5.82	$5.80	$5.80
Purchase #6	$181.52	4.143%	$189.0404	$189.04	$189.05	$189.00
Purchase #7	$66.30	7.444%	$71.2354	$71.24	$71.25	$71.20
7 purchase totals =	$791.46		$856.8942	$856.91	$856.90	$856.80