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	$93.93	5.590%	$99.1807	$99.18	$99.20	$99.20
Purchase #2	$185.82	3.790%	$192.8626	$192.86	$192.85	$192.90
Purchase #3	$97.76	10.765%	$108.2839	$108.28	$108.30	$108.30
Purchase #4	$196.53	9.661%	$215.5168	$215.52	$215.50	$215.50
Purchase #5	$11.55	5.176%	$12.1478	$12.15	$12.15	$12.10
Purchase #6	$140.83	13.113%	$159.297	$159.30	$159.30	$159.30
Purchase #7	$11.97	11.203%	$13.311	$13.31	$13.30	$13.30
7 purchase totals =	$738.39		$800.5998	$800.60	$800.60	$800.60