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	$72.53	8.674%	$78.8213	$78.82	$78.80	$78.80
Purchase #2	$90.77	10.307%	$100.1257	$100.13	$100.15	$100.10
Purchase #3	$192.68	10.288%	$212.5029	$212.50	$212.50	$212.50
Purchase #4	$158.34	11.683%	$176.8389	$176.84	$176.85	$176.80
Purchase #5	$203.72	3.365%	$210.5752	$210.58	$210.60	$210.60
Purchase #6	$6.37	3.818%	$6.6132	$6.61	$6.60	$6.60
Purchase #7	$105.27	13.788%	$119.7846	$119.78	$119.80	$119.80
7 purchase totals =	$829.68		$905.2618	$905.26	$905.30	$905.20