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	$246.53	12.814%	$278.1204	$278.12	$278.10	$278.10
Purchase #2	$47.45	3.786%	$49.2465	$49.25	$49.25	$49.20
Purchase #3	$126.49	6.227%	$134.3665	$134.37	$134.35	$134.40
Purchase #4	$19.59	6.537%	$20.8706	$20.87	$20.85	$20.90
Purchase #5	$71.65	7.201%	$76.8095	$76.81	$76.80	$76.80
Purchase #6	$58.80	6.334%	$62.5244	$62.52	$62.50	$62.50
Purchase #7	$39.80	9.410%	$43.5452	$43.55	$43.55	$43.50
7 purchase totals =	$610.31		$665.4831	$665.49	$665.40	$665.40