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	$30.88	9.733%	$33.8856	$33.89	$33.90	$33.90
Purchase #2	$114.82	7.446%	$123.3695	$123.37	$123.35	$123.40
Purchase #3	$19.70	9.544%	$21.5802	$21.58	$21.60	$21.60
Purchase #4	$42.71	5.627%	$45.1133	$45.11	$45.10	$45.10
Purchase #5	$81.28	7.470%	$87.3516	$87.35	$87.35	$87.40
Purchase #6	$9.78	11.534%	$10.908	$10.91	$10.90	$10.90
Purchase #7	$24.36	7.143%	$26.1	$26.10	$26.10	$26.10
7 purchase totals =	$323.53		$348.3082	$348.31	$348.30	$348.40