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	$36.94	9.426%	$40.422	$40.42	$40.40	$40.40
Purchase #2	$148.64	12.436%	$167.1249	$167.12	$167.10	$167.10
Purchase #3	$44.38	8.821%	$48.2948	$48.29	$48.30	$48.30
Purchase #4	$80.84	5.580%	$85.3509	$85.35	$85.35	$85.40
Purchase #5	$31.71	5.723%	$33.5248	$33.52	$33.50	$33.50
Purchase #6	$96.38	9.111%	$105.1612	$105.16	$105.15	$105.20
Purchase #7	$20.59	13.286%	$23.3256	$23.33	$23.35	$23.30
7 purchase totals =	$459.48		$503.2042	$503.19	$503.15	$503.20