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	$142.52	5.133%	$149.8356	$149.84	$149.85	$149.80
Purchase #2	$65.46	4.642%	$68.4987	$68.50	$68.50	$68.50
Purchase #3	$199.39	11.589%	$222.4973	$222.50	$222.50	$222.50
Purchase #4	$51.78	3.823%	$53.7595	$53.76	$53.75	$53.80
Purchase #5	$235.45	8.507%	$255.4797	$255.48	$255.50	$255.50
Purchase #6	$50.28	8.252%	$54.4291	$54.43	$54.45	$54.40
Purchase #7	$12.46	4.406%	$13.009	$13.01	$13.00	$13.00
7 purchase totals =	$757.34		$817.5089	$817.52	$817.55	$817.50