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	$15.87	6.460%	$16.8952	$16.90	$16.90	$16.90
Purchase #2	$40.32	4.834%	$42.2691	$42.27	$42.25	$42.30
Purchase #3	$103.39	6.340%	$109.9449	$109.94	$109.95	$109.90
Purchase #4	$71.55	10.309%	$78.9261	$78.93	$78.95	$78.90
Purchase #5	$23.31	5.311%	$24.548	$24.55	$24.55	$24.50
Purchase #6	$97.53	3.845%	$101.28	$101.28	$101.30	$101.30
Purchase #7	$137.61	13.620%	$156.3525	$156.35	$156.35	$156.40
7 purchase totals =	$489.58		$530.2158	$530.22	$530.25	$530.20