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	$16.76	3.333%	$17.3186	$17.32	$17.30	$17.30
Purchase #2	$24.65	11.189%	$27.4081	$27.41	$27.40	$27.40
Purchase #3	$132.49	11.616%	$147.88	$147.88	$147.90	$147.90
Purchase #4	$123.85	4.265%	$129.1322	$129.13	$129.15	$129.10
Purchase #5	$82.60	6.848%	$88.2564	$88.26	$88.25	$88.30
Purchase #6	$82.29	10.372%	$90.8251	$90.83	$90.85	$90.80
Purchase #7	$169.89	12.174%	$190.5724	$190.57	$190.55	$190.60
7 purchase totals =	$632.53		$691.3928	$691.40	$691.40	$691.40