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	$26.52	3.508%	$27.4503	$27.45	$27.45	$27.50
Purchase #2	$160.91	3.467%	$166.4887	$166.49	$166.50	$166.50
Purchase #3	$95.44	5.661%	$100.8429	$100.84	$100.85	$100.80
Purchase #4	$239.63	4.612%	$250.6817	$250.68	$250.70	$250.70
Purchase #5	$12.95	11.180%	$14.3978	$14.40	$14.40	$14.40
Purchase #6	$78.54	8.340%	$85.0902	$85.09	$85.10	$85.10
Purchase #7	$130.43	7.753%	$140.5422	$140.54	$140.55	$140.50
7 purchase totals =	$744.42		$785.4938	$785.49	$785.55	$785.50