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	$96.92	6.184%	$102.9135	$102.91	$102.90	$102.90
Purchase #2	$49.29	8.711%	$53.5837	$53.58	$53.60	$53.60
Purchase #3	$188.55	4.212%	$196.4917	$196.49	$196.50	$196.50
Purchase #4	$44.32	12.113%	$49.6885	$49.69	$49.70	$49.70
Purchase #5	$178.41	10.313%	$196.8094	$196.81	$196.80	$196.80
Purchase #6	$185.68	4.710%	$194.4255	$194.43	$194.45	$194.40
Purchase #7	$22.70	9.159%	$24.7791	$24.78	$24.80	$24.80
7 purchase totals =	$765.87		$818.6914	$818.69	$818.75	$818.70