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	$109.98	12.134%	$123.325	$123.33	$123.35	$123.30
Purchase #2	$244.42	10.577%	$270.2723	$270.27	$270.25	$270.30
Purchase #3	$66.50	11.677%	$74.2652	$74.27	$74.25	$74.30
Purchase #4	$235.82	7.742%	$254.0772	$254.08	$254.10	$254.10
Purchase #5	$72.60	9.650%	$79.6059	$79.61	$79.60	$79.60
Purchase #6	$46.71	11.166%	$51.9256	$51.93	$51.95	$51.90
Purchase #7	$144.29	8.128%	$156.0179	$156.02	$156.00	$156.00
7 purchase totals =	$920.32		$1,009.4891	$1,009.51	$1,009.50	$1,009.50