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	$16.36	8.535%	$17.7563	$17.76	$17.75	$17.80
Purchase #2	$64.76	3.335%	$66.9197	$66.92	$66.90	$66.90
Purchase #3	$133.61	10.335%	$147.4186	$147.42	$147.40	$147.40
Purchase #4	$200.78	7.341%	$215.5193	$215.52	$215.50	$215.50
Purchase #5	$172.85	13.623%	$196.3974	$196.40	$196.40	$196.40
Purchase #6	$228.94	9.628%	$250.9823	$250.98	$251.00	$251.00
Purchase #7	$224.55	13.121%	$254.0132	$254.01	$254.00	$254.00
7 purchase totals =	$1,041.85		$1,149.0068	$1,149.01	$1,148.95	$1,149.00