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	$85.60	5.519%	$90.3243	$90.32	$90.30	$90.30
Purchase #2	$95.45	12.499%	$107.3803	$107.38	$107.40	$107.40
Purchase #3	$102.37	4.361%	$106.8344	$106.83	$106.85	$106.80
Purchase #4	$45.56	7.311%	$48.8909	$48.89	$48.90	$48.90
Purchase #5	$143.75	10.741%	$159.1902	$159.19	$159.20	$159.20
Purchase #6	$42.49	4.709%	$44.4909	$44.49	$44.50	$44.50
Purchase #7	$121.32	5.720%	$128.2595	$128.26	$128.25	$128.30
7 purchase totals =	$636.54		$685.3705	$685.36	$685.40	$685.40