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	$36.43	11.655%	$40.6759	$40.68	$40.70	$40.70
Purchase #2	$151.84	5.407%	$160.05	$160.05	$160.05	$160.10
Purchase #3	$76.52	11.436%	$85.2708	$85.27	$85.25	$85.30
Purchase #4	$34.42	4.363%	$35.9217	$35.92	$35.90	$35.90
Purchase #5	$162.93	13.808%	$185.4274	$185.43	$185.45	$185.40
Purchase #6	$37.90	3.511%	$39.2307	$39.23	$39.25	$39.20
Purchase #7	$155.99	12.604%	$175.651	$175.65	$175.65	$175.70
7 purchase totals =	$656.03		$722.2275	$722.23	$722.25	$722.30