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	$160.73	11.380%	$179.0211	$179.02	$179.00	$179.00
Purchase #2	$73.51	7.367%	$78.9255	$78.93	$78.95	$78.90
Purchase #3	$46.96	4.446%	$49.0478	$49.05	$49.05	$49.00
Purchase #4	$178.55	5.598%	$188.5452	$188.55	$188.55	$188.50
Purchase #5	$41.35	3.789%	$42.9168	$42.92	$42.90	$42.90
Purchase #6	$156.48	5.694%	$165.39	$165.39	$165.40	$165.40
Purchase #7	$197.49	10.513%	$218.2521	$218.25	$218.25	$218.30
7 purchase totals =	$855.07		$922.0985	$922.11	$922.10	$922.00