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	$91.44	10.347%	$100.9013	$100.90	$100.90	$100.90
Purchase #2	$40.89	5.833%	$43.2751	$43.28	$43.30	$43.30
Purchase #3	$245.78	3.727%	$254.9402	$254.94	$254.95	$254.90
Purchase #4	$199.61	9.592%	$218.7566	$218.76	$218.75	$218.80
Purchase #5	$121.93	4.685%	$127.6424	$127.64	$127.65	$127.60
Purchase #6	$31.40	10.399%	$34.6653	$34.67	$34.65	$34.70
Purchase #7	$66.32	5.144%	$69.7315	$69.73	$69.75	$69.70
7 purchase totals =	$797.37		$849.9124	$849.92	$849.95	$849.90