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	$122.39	7.517%	$131.5901	$131.59	$131.60	$131.60
Purchase #2	$37.92	13.125%	$42.897	$42.90	$42.90	$42.90
Purchase #3	$41.77	11.171%	$46.4361	$46.44	$46.45	$46.40
Purchase #4	$142.69	13.202%	$161.5279	$161.53	$161.55	$161.50
Purchase #5	$247.82	5.589%	$261.6707	$261.67	$261.65	$261.70
Purchase #6	$16.91	9.599%	$18.5332	$18.53	$18.55	$18.50
Purchase #7	$230.40	3.351%	$238.1207	$238.12	$238.10	$238.10
7 purchase totals =	$839.90		$900.7757	$900.78	$900.80	$900.70