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	$53.80	9.796%	$59.0702	$59.07	$59.05	$59.10
Purchase #2	$247.76	11.815%	$277.0328	$277.03	$277.05	$277.00
Purchase #3	$242.35	6.874%	$259.0091	$259.01	$259.00	$259.00
Purchase #4	$142.40	8.291%	$154.2064	$154.21	$154.20	$154.20
Purchase #5	$137.39	10.288%	$151.5247	$151.52	$151.50	$151.50
Purchase #6	$250.30	9.129%	$273.1499	$273.15	$273.15	$273.10
Purchase #7	$89.94	6.634%	$95.9066	$95.91	$95.90	$95.90
7 purchase totals =	$1,163.94		$1,269.8997	$1,269.90	$1,269.85	$1,269.80