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	$152.34	7.831%	$164.2697	$164.27	$164.25	$164.30
Purchase #2	$153.75	7.589%	$165.4181	$165.42	$165.40	$165.40
Purchase #3	$42.84	10.316%	$47.2594	$47.26	$47.25	$47.30
Purchase #4	$41.64	5.302%	$43.8478	$43.85	$43.85	$43.80
Purchase #5	$122.57	8.514%	$133.0056	$133.01	$133.00	$133.00
Purchase #6	$17.49	9.343%	$19.1241	$19.12	$19.10	$19.10
Purchase #7	$82.46	9.726%	$90.4801	$90.48	$90.50	$90.50
7 purchase totals =	$613.09		$663.4048	$663.41	$663.35	$663.40