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	$35.93	6.464%	$38.2525	$38.25	$38.25	$38.30
Purchase #2	$247.80	12.361%	$278.4306	$278.43	$278.45	$278.40
Purchase #3	$153.51	11.422%	$171.0439	$171.04	$171.05	$171.00
Purchase #4	$237.84	12.552%	$267.6937	$267.69	$267.70	$267.70
Purchase #5	$68.68	5.641%	$72.5542	$72.55	$72.55	$72.60
Purchase #6	$70.65	11.538%	$78.8016	$78.80	$78.80	$78.80
Purchase #7	$193.44	5.637%	$204.3442	$204.34	$204.35	$204.30
7 purchase totals =	$1,007.85		$1,111.1207	$1,111.10	$1,111.15	$1,111.10