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	$133.97	4.268%	$139.6878	$139.69	$139.70	$139.70
Purchase #2	$133.34	6.568%	$142.0978	$142.10	$142.10	$142.10
Purchase #3	$135.73	10.681%	$150.2273	$150.23	$150.25	$150.20
Purchase #4	$69.53	5.608%	$73.4292	$73.43	$73.45	$73.40
Purchase #5	$37.75	8.791%	$41.0686	$41.07	$41.05	$41.10
Purchase #6	$230.67	4.602%	$241.2854	$241.29	$241.30	$241.30
Purchase #7	$123.28	3.578%	$127.691	$127.69	$127.70	$127.70
7 purchase totals =	$864.27		$915.4871	$915.50	$915.55	$915.50