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	$231.85	3.731%	$240.5003	$240.50	$240.50	$240.50
Purchase #2	$81.63	13.822%	$92.9129	$92.91	$92.90	$92.90
Purchase #3	$83.87	10.737%	$92.8751	$92.88	$92.90	$92.90
Purchase #4	$40.66	5.162%	$42.7589	$42.76	$42.75	$42.80
Purchase #5	$119.57	8.647%	$129.9092	$129.91	$129.90	$129.90
Purchase #6	$133.87	9.427%	$146.4899	$146.49	$146.50	$146.50
Purchase #7	$12.85	9.527%	$14.0742	$14.07	$14.05	$14.10
7 purchase totals =	$704.30		$759.5205	$759.52	$759.50	$759.60