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	$88.41	12.376%	$99.3516	$99.35	$99.35	$99.40
Purchase #2	$105.70	8.214%	$114.3822	$114.38	$114.40	$114.40
Purchase #3	$196.88	10.665%	$217.8773	$217.88	$217.90	$217.90
Purchase #4	$140.32	4.624%	$146.8084	$146.81	$146.80	$146.80
Purchase #5	$129.42	12.486%	$145.5794	$145.58	$145.60	$145.60
Purchase #6	$128.93	10.270%	$142.1711	$142.17	$142.15	$142.20
Purchase #7	$188.71	3.324%	$194.9827	$194.98	$195.00	$195.00
7 purchase totals =	$978.37		$1,061.1527	$1,061.15	$1,061.20	$1,061.30