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	$97.46	6.626%	$103.9177	$103.92	$103.90	$103.90
Purchase #2	$73.53	10.509%	$81.2573	$81.26	$81.25	$81.30
Purchase #3	$37.42	9.354%	$40.9203	$40.92	$40.90	$40.90
Purchase #4	$54.64	10.832%	$60.5586	$60.56	$60.55	$60.60
Purchase #5	$13.65	8.540%	$14.8157	$14.82	$14.80	$14.80
Purchase #6	$63.76	5.323%	$67.1539	$67.15	$67.15	$67.20
Purchase #7	$54.52	10.815%	$60.4163	$60.42	$60.40	$60.40
7 purchase totals =	$394.98		$429.0398	$429.05	$428.95	$429.10