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	$74.46	11.579%	$83.0817	$83.08	$83.10	$83.10
Purchase #2	$58.59	6.233%	$62.2419	$62.24	$62.25	$62.20
Purchase #3	$104.47	13.739%	$118.8231	$118.82	$118.80	$118.80
Purchase #4	$54.59	4.874%	$57.2507	$57.25	$57.25	$57.30
Purchase #5	$169.31	7.669%	$182.2944	$182.29	$182.30	$182.30
Purchase #6	$42.85	9.580%	$46.955	$46.96	$46.95	$47.00
Purchase #7	$21.59	10.454%	$23.847	$23.85	$23.85	$23.80
7 purchase totals =	$525.86		$574.4938	$574.49	$574.50	$574.50