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	$247.86	3.466%	$256.4508	$256.45	$256.45	$256.50
Purchase #2	$99.56	12.518%	$112.0229	$112.02	$112.00	$112.00
Purchase #3	$26.91	6.291%	$28.6029	$28.60	$28.60	$28.60
Purchase #4	$21.81	11.713%	$24.3646	$24.36	$24.35	$24.40
Purchase #5	$181.51	9.822%	$199.3379	$199.34	$199.35	$199.30
Purchase #6	$165.76	9.767%	$181.9498	$181.95	$181.95	$181.90
Purchase #7	$90.30	5.753%	$95.495	$95.50	$95.50	$95.50
7 purchase totals =	$833.71		$898.2239	$898.22	$898.20	$898.20