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	$39.42	9.640%	$43.2201	$43.22	$43.20	$43.20
Purchase #2	$70.51	3.350%	$72.8721	$72.87	$72.85	$72.90
Purchase #3	$31.54	12.425%	$35.4588	$35.46	$35.45	$35.50
Purchase #4	$214.80	13.328%	$243.4285	$243.43	$243.45	$243.40
Purchase #5	$107.83	3.404%	$111.5005	$111.50	$111.50	$111.50
Purchase #6	$41.56	8.686%	$45.1699	$45.17	$45.15	$45.20
Purchase #7	$212.27	6.634%	$226.352	$226.35	$226.35	$226.40
7 purchase totals =	$717.93		$778.0019	$778.00	$777.95	$778.10