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	$83.73	5.580%	$88.4021	$88.40	$88.40	$88.40
Purchase #2	$176.38	6.638%	$188.0881	$188.09	$188.10	$188.10
Purchase #3	$74.58	10.489%	$82.4027	$82.40	$82.40	$82.40
Purchase #4	$76.82	12.321%	$86.285	$86.29	$86.30	$86.30
Purchase #5	$127.43	9.678%	$139.7627	$139.76	$139.75	$139.80
Purchase #6	$228.91	8.477%	$248.3147	$248.31	$248.30	$248.30
Purchase #7	$150.70	10.770%	$166.9304	$166.93	$166.95	$166.90
7 purchase totals =	$918.55		$1,000.1857	$1,000.18	$1,000.20	$1,000.20