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	$66.72	4.748%	$69.8879	$69.89	$69.90	$69.90
Purchase #2	$59.90	7.386%	$64.3242	$64.32	$64.30	$64.30
Purchase #3	$151.31	3.399%	$156.453	$156.45	$156.45	$156.50
Purchase #4	$101.37	7.672%	$109.1471	$109.15	$109.15	$109.10
Purchase #5	$80.63	7.842%	$86.953	$86.95	$86.95	$87.00
Purchase #6	$104.30	12.762%	$117.6108	$117.61	$117.60	$117.60
Purchase #7	$241.83	9.850%	$265.6503	$265.65	$265.65	$265.70
7 purchase totals =	$806.06		$870.0263	$870.02	$870.00	$870.10