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	$68.45	8.654%	$74.3737	$74.37	$74.35	$74.40
Purchase #2	$180.76	8.457%	$196.0469	$196.05	$196.05	$196.00
Purchase #3	$127.82	7.411%	$137.2927	$137.29	$137.30	$137.30
Purchase #4	$39.57	12.211%	$44.4019	$44.40	$44.40	$44.40
Purchase #5	$205.92	5.144%	$216.5125	$216.51	$216.50	$216.50
Purchase #6	$112.25	12.598%	$126.3913	$126.39	$126.40	$126.40
Purchase #7	$108.71	13.727%	$123.6326	$123.63	$123.65	$123.60
7 purchase totals =	$843.48		$918.6516	$918.64	$918.65	$918.60