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	$186.30	7.629%	$200.5128	$200.51	$200.50	$200.50
Purchase #2	$59.91	10.394%	$66.137	$66.14	$66.15	$66.10
Purchase #3	$118.40	10.850%	$131.2464	$131.25	$131.25	$131.20
Purchase #4	$188.77	11.506%	$210.4899	$210.49	$210.50	$210.50
Purchase #5	$179.99	11.545%	$200.7698	$200.77	$200.75	$200.80
Purchase #6	$58.45	9.837%	$64.1997	$64.20	$64.20	$64.20
Purchase #7	$26.40	6.414%	$28.0933	$28.09	$28.10	$28.10
7 purchase totals =	$818.22		$901.4489	$901.45	$901.45	$901.40