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	$155.70	10.337%	$171.7947	$171.79	$171.80	$171.80
Purchase #2	$172.98	3.305%	$178.697	$178.70	$178.70	$178.70
Purchase #3	$111.47	10.793%	$123.501	$123.50	$123.50	$123.50
Purchase #4	$168.83	5.840%	$178.6897	$178.69	$178.70	$178.70
Purchase #5	$142.65	7.739%	$153.6897	$153.69	$153.70	$153.70
Purchase #6	$66.83	6.829%	$71.3938	$71.39	$71.40	$71.40
Purchase #7	$179.38	5.760%	$189.7123	$189.71	$189.70	$189.70
7 purchase totals =	$997.84		$1,067.4782	$1,067.47	$1,067.50	$1,067.50