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	$7.89	9.609%	$8.6482	$8.65	$8.65	$8.60
Purchase #2	$50.50	10.178%	$55.6399	$55.64	$55.65	$55.60
Purchase #3	$92.91	8.152%	$100.484	$100.48	$100.50	$100.50
Purchase #4	$166.78	12.158%	$187.0571	$187.06	$187.05	$187.10
Purchase #5	$107.81	11.188%	$119.8718	$119.87	$119.85	$119.90
Purchase #6	$7.33	13.631%	$8.3292	$8.33	$8.35	$8.30
Purchase #7	$19.29	3.160%	$19.8996	$19.90	$19.90	$19.90
7 purchase totals =	$452.51		$499.9298	$499.93	$499.95	$499.90