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	$90.39	12.239%	$101.4528	$101.45	$101.45	$101.50
Purchase #2	$38.66	7.788%	$41.6708	$41.67	$41.65	$41.70
Purchase #3	$107.59	6.665%	$114.7609	$114.76	$114.75	$114.80
Purchase #4	$93.51	11.833%	$104.575	$104.58	$104.60	$104.60
Purchase #5	$49.98	11.361%	$55.6582	$55.66	$55.65	$55.70
Purchase #6	$97.25	4.538%	$101.6632	$101.66	$101.65	$101.70
Purchase #7	$105.64	3.661%	$109.5075	$109.51	$109.50	$109.50
7 purchase totals =	$583.02		$629.2884	$629.29	$629.25	$629.50