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	$93.94	5.699%	$99.2936	$99.29	$99.30	$99.30
Purchase #2	$137.69	13.782%	$156.6664	$156.67	$156.65	$156.70
Purchase #3	$167.54	13.167%	$189.6	$189.60	$189.60	$189.60
Purchase #4	$137.58	9.201%	$150.2387	$150.24	$150.25	$150.20
Purchase #5	$105.89	11.508%	$118.0758	$118.08	$118.10	$118.10
Purchase #6	$160.37	7.602%	$172.5613	$172.56	$172.55	$172.60
Purchase #7	$37.42	10.290%	$41.2705	$41.27	$41.25	$41.30
7 purchase totals =	$840.43		$927.7063	$927.71	$927.70	$927.80