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	$131.78	11.139%	$146.459	$146.46	$146.45	$146.50
Purchase #2	$186.52	5.848%	$197.4277	$197.43	$197.45	$197.40
Purchase #3	$6.87	10.619%	$7.5995	$7.60	$7.60	$7.60
Purchase #4	$67.98	10.208%	$74.9194	$74.92	$74.90	$74.90
Purchase #5	$45.63	4.853%	$47.8444	$47.84	$47.85	$47.80
Purchase #6	$55.43	3.660%	$57.4587	$57.46	$57.45	$57.50
Purchase #7	$81.77	9.122%	$89.2291	$89.23	$89.25	$89.20
7 purchase totals =	$575.98		$620.9378	$620.94	$620.95	$620.90