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	$131.53	5.784%	$139.1377	$139.14	$139.15	$139.10
Purchase #2	$87.41	4.662%	$91.4851	$91.49	$91.50	$91.50
Purchase #3	$7.96	10.739%	$8.8148	$8.81	$8.80	$8.80
Purchase #4	$132.39	11.452%	$147.5513	$147.55	$147.55	$147.60
Purchase #5	$127.64	13.483%	$144.8497	$144.85	$144.85	$144.80
Purchase #6	$186.92	5.234%	$196.7034	$196.70	$196.70	$196.70
Purchase #7	$124.47	7.643%	$133.9832	$133.98	$134.00	$134.00
7 purchase totals =	$798.32		$862.5252	$862.52	$862.55	$862.50