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	$156.52	5.861%	$165.6936	$165.69	$165.70	$165.70
Purchase #2	$125.63	5.365%	$132.37	$132.37	$132.35	$132.40
Purchase #3	$122.41	4.272%	$127.6394	$127.64	$127.65	$127.60
Purchase #4	$239.44	4.466%	$250.1334	$250.13	$250.15	$250.10
Purchase #5	$45.59	13.610%	$51.7948	$51.79	$51.80	$51.80
Purchase #6	$108.48	8.218%	$117.3949	$117.39	$117.40	$117.40
Purchase #7	$123.71	5.778%	$130.858	$130.86	$130.85	$130.90
7 purchase totals =	$921.78		$975.8841	$975.87	$975.90	$975.90