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	$80.29	6.723%	$85.6879	$85.69	$85.70	$85.70
Purchase #2	$29.80	11.372%	$33.1889	$33.19	$33.20	$33.20
Purchase #3	$177.53	8.383%	$192.4123	$192.41	$192.40	$192.40
Purchase #4	$219.45	5.546%	$231.6207	$231.62	$231.60	$231.60
Purchase #5	$26.59	6.251%	$28.2521	$28.25	$28.25	$28.30
Purchase #6	$41.29	6.358%	$43.9152	$43.92	$43.90	$43.90
Purchase #7	$246.42	11.755%	$275.3867	$275.39	$275.40	$275.40
7 purchase totals =	$821.37		$890.4638	$890.47	$890.45	$890.50