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	$133.41	7.579%	$143.5211	$143.52	$143.50	$143.50
Purchase #2	$127.47	11.403%	$142.0054	$142.01	$142.00	$142.00
Purchase #3	$167.90	6.215%	$178.335	$178.34	$178.35	$178.30
Purchase #4	$77.97	6.833%	$83.2977	$83.30	$83.30	$83.30
Purchase #5	$90.27	8.224%	$97.6938	$97.69	$97.70	$97.70
Purchase #6	$18.94	6.148%	$20.1044	$20.10	$20.10	$20.10
Purchase #7	$187.94	12.529%	$211.487	$211.49	$211.50	$211.50
7 purchase totals =	$803.90		$876.4444	$876.45	$876.45	$876.40