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	$50.25	6.708%	$53.6208	$53.62	$53.60	$53.60
Purchase #2	$87.86	4.611%	$91.9112	$91.91	$91.90	$91.90
Purchase #3	$205.32	5.360%	$216.3252	$216.33	$216.35	$216.30
Purchase #4	$87.25	3.586%	$90.3788	$90.38	$90.40	$90.40
Purchase #5	$67.49	13.269%	$76.4452	$76.45	$76.45	$76.40
Purchase #6	$36.89	10.163%	$40.6391	$40.64	$40.65	$40.60
Purchase #7	$40.39	6.160%	$42.878	$42.88	$42.90	$42.90
7 purchase totals =	$575.45		$612.1983	$612.21	$612.25	$612.10