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	$40.67	7.187%	$43.593	$43.59	$43.60	$43.60
Purchase #2	$138.79	12.224%	$155.7557	$155.76	$155.75	$155.80
Purchase #3	$67.92	5.555%	$71.693	$71.69	$71.70	$71.70
Purchase #4	$188.40	8.200%	$203.8488	$203.85	$203.85	$203.80
Purchase #5	$167.75	11.634%	$187.266	$187.27	$187.25	$187.30
Purchase #6	$81.47	9.727%	$89.3946	$89.39	$89.40	$89.40
Purchase #7	$170.89	7.210%	$183.2112	$183.21	$183.20	$183.20
7 purchase totals =	$855.89		$934.7623	$934.76	$934.75	$934.80