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	$76.49	9.575%	$83.8139	$83.81	$83.80	$83.80
Purchase #2	$219.59	8.536%	$238.3342	$238.33	$238.35	$238.30
Purchase #3	$43.66	7.110%	$46.7642	$46.76	$46.75	$46.80
Purchase #4	$61.83	9.733%	$67.8479	$67.85	$67.85	$67.80
Purchase #5	$157.56	13.294%	$178.506	$178.51	$178.50	$178.50
Purchase #6	$36.79	9.719%	$40.3656	$40.37	$40.35	$40.40
Purchase #7	$93.41	5.156%	$98.2262	$98.23	$98.25	$98.20
7 purchase totals =	$689.33		$753.8580	$753.86	$753.85	$753.80