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	$163.40	10.513%	$180.5782	$180.58	$180.60	$180.60
Purchase #2	$48.82	13.867%	$55.5899	$55.59	$55.60	$55.60
Purchase #3	$204.25	11.226%	$227.1791	$227.18	$227.20	$227.20
Purchase #4	$72.92	7.156%	$78.1382	$78.14	$78.15	$78.10
Purchase #5	$52.80	5.231%	$55.562	$55.56	$55.55	$55.60
Purchase #6	$163.59	10.399%	$180.6017	$180.60	$180.60	$180.60
Purchase #7	$61.61	8.856%	$67.0662	$67.07	$67.05	$67.10
7 purchase totals =	$767.39		$844.7153	$844.72	$844.75	$844.80