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	$18.45	5.749%	$19.5107	$19.51	$19.50	$19.50
Purchase #2	$88.28	13.593%	$100.2799	$100.28	$100.30	$100.30
Purchase #3	$34.41	10.673%	$38.0826	$38.08	$38.10	$38.10
Purchase #4	$97.56	6.632%	$104.0302	$104.03	$104.05	$104.00
Purchase #5	$97.81	12.175%	$109.7184	$109.72	$109.70	$109.70
Purchase #6	$168.28	13.315%	$190.6865	$190.69	$190.70	$190.70
Purchase #7	$140.28	10.760%	$155.3741	$155.37	$155.35	$155.40
7 purchase totals =	$645.07		$717.6824	$717.68	$717.70	$717.70