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	$29.88	13.446%	$33.8977	$33.90	$33.90	$33.90
Purchase #2	$213.68	7.820%	$230.3898	$230.39	$230.40	$230.40
Purchase #3	$147.33	9.623%	$161.5076	$161.51	$161.50	$161.50
Purchase #4	$82.35	10.373%	$90.8922	$90.89	$90.90	$90.90
Purchase #5	$231.73	7.512%	$249.1376	$249.14	$249.15	$249.10
Purchase #6	$183.77	9.583%	$201.3807	$201.38	$201.40	$201.40
Purchase #7	$139.98	7.733%	$150.8047	$150.80	$150.80	$150.80
7 purchase totals =	$1,028.72		$1,118.0103	$1,118.01	$1,118.05	$1,118.00