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	$97.75	13.605%	$111.0489	$111.05	$111.05	$111.00
Purchase #2	$37.64	12.615%	$42.3883	$42.39	$42.40	$42.40
Purchase #3	$89.44	5.149%	$94.0453	$94.05	$94.05	$94.00
Purchase #4	$36.90	9.209%	$40.2981	$40.30	$40.30	$40.30
Purchase #5	$74.90	4.328%	$78.1417	$78.14	$78.15	$78.10
Purchase #6	$166.42	10.491%	$183.8791	$183.88	$183.90	$183.90
Purchase #7	$35.96	5.457%	$37.9223	$37.92	$37.90	$37.90
7 purchase totals =	$539.01		$587.7237	$587.73	$587.75	$587.60