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	$30.77	10.219%	$33.9144	$33.91	$33.90	$33.90
Purchase #2	$55.81	12.805%	$62.9565	$62.96	$62.95	$63.00
Purchase #3	$151.52	7.789%	$163.3219	$163.32	$163.30	$163.30
Purchase #4	$15.79	4.870%	$16.559	$16.56	$16.55	$16.60
Purchase #5	$70.78	10.718%	$78.3662	$78.37	$78.35	$78.40
Purchase #6	$82.56	3.408%	$85.3736	$85.37	$85.35	$85.40
Purchase #7	$192.25	4.363%	$200.6379	$200.64	$200.65	$200.60
7 purchase totals =	$599.48		$641.1295	$641.13	$641.05	$641.20