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	$85.90	4.622%	$89.8703	$89.87	$89.85	$89.90
Purchase #2	$172.78	7.464%	$185.6763	$185.68	$185.70	$185.70
Purchase #3	$115.89	4.626%	$121.2511	$121.25	$121.25	$121.30
Purchase #4	$84.97	12.298%	$95.4196	$95.42	$95.40	$95.40
Purchase #5	$159.65	7.727%	$171.9862	$171.99	$172.00	$172.00
Purchase #6	$132.37	13.640%	$150.4253	$150.43	$150.45	$150.40
Purchase #7	$248.66	11.497%	$277.2484	$277.25	$277.25	$277.20
7 purchase totals =	$1,000.22		$1,091.8772	$1,091.89	$1,091.90	$1,091.90