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	$100.43	8.751%	$109.2186	$109.22	$109.20	$109.20
Purchase #2	$185.68	6.640%	$198.0092	$198.01	$198.00	$198.00
Purchase #3	$224.41	3.332%	$231.8873	$231.89	$231.90	$231.90
Purchase #4	$65.43	11.451%	$72.9224	$72.92	$72.90	$72.90
Purchase #5	$112.53	3.143%	$116.0668	$116.07	$116.05	$116.10
Purchase #6	$116.30	10.757%	$128.8104	$128.81	$128.80	$128.80
Purchase #7	$50.69	8.735%	$55.1178	$55.12	$55.10	$55.10
7 purchase totals =	$855.47		$912.0325	$912.04	$911.95	$912.00