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	$15.25	13.231%	$17.2677	$17.27	$17.25	$17.30
Purchase #2	$146.82	12.246%	$164.7996	$164.80	$164.80	$164.80
Purchase #3	$22.43	8.122%	$24.2518	$24.25	$24.25	$24.30
Purchase #4	$68.99	13.196%	$78.0939	$78.09	$78.10	$78.10
Purchase #5	$59.82	7.657%	$64.4004	$64.40	$64.40	$64.40
Purchase #6	$89.79	10.136%	$98.8911	$98.89	$98.90	$98.90
Purchase #7	$200.67	7.334%	$215.3871	$215.39	$215.40	$215.40
7 purchase totals =	$603.77		$663.0916	$663.09	$663.10	$663.20