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	$5.92	13.718%	$6.7321	$6.73	$6.75	$6.70
Purchase #2	$25.56	12.721%	$28.8115	$28.81	$28.80	$28.80
Purchase #3	$230.30	3.575%	$238.5332	$238.53	$238.55	$238.50
Purchase #4	$119.51	6.709%	$127.5279	$127.53	$127.55	$127.50
Purchase #5	$18.62	9.814%	$20.4474	$20.45	$20.45	$20.40
Purchase #6	$22.89	5.381%	$24.1217	$24.12	$24.10	$24.10
Purchase #7	$169.51	8.336%	$183.6404	$183.64	$183.65	$183.60
7 purchase totals =	$592.31		$629.8142	$629.81	$629.85	$629.60