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	$47.50	7.371%	$51.0012	$51.00	$51.00	$51.00
Purchase #2	$230.27	7.155%	$246.7458	$246.75	$246.75	$246.70
Purchase #3	$65.56	10.585%	$72.4995	$72.50	$72.50	$72.50
Purchase #4	$90.70	5.363%	$95.5642	$95.56	$95.55	$95.60
Purchase #5	$180.34	10.719%	$199.6706	$199.67	$199.65	$199.70
Purchase #6	$151.54	10.571%	$167.5593	$167.56	$167.55	$167.60
Purchase #7	$170.69	4.597%	$178.5366	$178.54	$178.55	$178.50
7 purchase totals =	$936.60		$1,011.5772	$1,011.58	$1,011.55	$1,011.60