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	$186.78	10.500%	$206.3919	$206.39	$206.40	$206.40
Purchase #2	$94.90	5.553%	$100.1698	$100.17	$100.15	$100.20
Purchase #3	$12.30	12.579%	$13.8472	$13.85	$13.85	$13.80
Purchase #4	$116.95	12.203%	$131.2214	$131.22	$131.20	$131.20
Purchase #5	$231.92	3.347%	$239.6824	$239.68	$239.70	$239.70
Purchase #6	$229.49	11.524%	$255.9364	$255.94	$255.95	$255.90
Purchase #7	$63.90	11.736%	$71.3993	$71.40	$71.40	$71.40
7 purchase totals =	$936.24		$1,018.6484	$1,018.65	$1,018.65	$1,018.60