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	$70.85	6.524%	$75.4723	$75.47	$75.45	$75.50
Purchase #2	$200.77	13.219%	$227.3098	$227.31	$227.30	$227.30
Purchase #3	$36.52	4.607%	$38.2025	$38.20	$38.20	$38.20
Purchase #4	$30.37	3.675%	$31.4861	$31.49	$31.50	$31.50
Purchase #5	$195.68	6.296%	$208	$208.00	$208.00	$208.00
Purchase #6	$41.54	4.334%	$43.3403	$43.34	$43.35	$43.30
Purchase #7	$198.66	12.175%	$222.8469	$222.85	$222.85	$222.80
7 purchase totals =	$774.39		$846.6579	$846.66	$846.65	$846.60