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	$76.70	11.520%	$85.5358	$85.54	$85.55	$85.50
Purchase #2	$118.78	3.543%	$122.9884	$122.99	$123.00	$123.00
Purchase #3	$247.50	12.868%	$279.3483	$279.35	$279.35	$279.30
Purchase #4	$106.96	5.526%	$112.8706	$112.87	$112.85	$112.90
Purchase #5	$14.46	6.620%	$15.4173	$15.42	$15.40	$15.40
Purchase #6	$66.42	8.275%	$71.9163	$71.92	$71.90	$71.90
Purchase #7	$143.34	9.743%	$157.3056	$157.31	$157.30	$157.30
7 purchase totals =	$774.16		$845.3823	$845.40	$845.35	$845.30