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	$107.64	7.694%	$115.9218	$115.92	$115.90	$115.90
Purchase #2	$96.41	10.212%	$106.2554	$106.26	$106.25	$106.30
Purchase #3	$35.43	6.758%	$37.8244	$37.82	$37.80	$37.80
Purchase #4	$63.58	13.534%	$72.1849	$72.18	$72.20	$72.20
Purchase #5	$134.67	6.831%	$143.8693	$143.87	$143.85	$143.90
Purchase #6	$60.67	10.791%	$67.2169	$67.22	$67.20	$67.20
Purchase #7	$115.29	9.840%	$126.6345	$126.63	$126.65	$126.60
7 purchase totals =	$613.69		$669.9072	$669.90	$669.85	$669.90