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	$117.66	3.463%	$121.7346	$121.73	$121.75	$121.70
Purchase #2	$90.73	11.103%	$100.8038	$100.80	$100.80	$100.80
Purchase #3	$194.46	7.286%	$208.6284	$208.63	$208.65	$208.60
Purchase #4	$187.57	3.742%	$194.5889	$194.59	$194.60	$194.60
Purchase #5	$94.64	9.445%	$103.5787	$103.58	$103.60	$103.60
Purchase #6	$199.88	6.193%	$212.2586	$212.26	$212.25	$212.30
Purchase #7	$72.70	8.415%	$78.8177	$78.82	$78.80	$78.80
7 purchase totals =	$957.64		$1,020.4107	$1,020.41	$1,020.45	$1,020.40