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	$113.55	6.113%	$120.4913	$120.49	$120.50	$120.50
Purchase #2	$177.72	5.419%	$187.3506	$187.35	$187.35	$187.40
Purchase #3	$147.94	13.244%	$167.5332	$167.53	$167.55	$167.50
Purchase #4	$16.47	13.407%	$18.6781	$18.68	$18.70	$18.70
Purchase #5	$30.64	6.328%	$32.5789	$32.58	$32.60	$32.60
Purchase #6	$39.35	4.754%	$41.2207	$41.22	$41.20	$41.20
Purchase #7	$37.68	11.467%	$42.0008	$42.00	$42.00	$42.00
7 purchase totals =	$563.35		$609.8536	$609.85	$609.90	$609.90