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	$234.66	8.727%	$255.1388	$255.14	$255.15	$255.10
Purchase #2	$26.83	3.711%	$27.8257	$27.83	$27.85	$27.80
Purchase #3	$226.28	8.457%	$245.4165	$245.42	$245.40	$245.40
Purchase #4	$21.36	9.371%	$23.3616	$23.36	$23.35	$23.40
Purchase #5	$87.27	6.406%	$92.8605	$92.86	$92.85	$92.90
Purchase #6	$111.32	11.278%	$123.8747	$123.87	$123.85	$123.90
Purchase #7	$150.38	11.644%	$167.8902	$167.89	$167.90	$167.90
7 purchase totals =	$858.10		$936.3680	$936.37	$936.35	$936.40