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	$185.31	6.449%	$197.2606	$197.26	$197.25	$197.30
Purchase #2	$54.82	7.636%	$59.0061	$59.01	$59.00	$59.00
Purchase #3	$192.90	8.459%	$209.2174	$209.22	$209.20	$209.20
Purchase #4	$221.69	13.519%	$251.6603	$251.66	$251.65	$251.70
Purchase #5	$65.25	11.658%	$72.8568	$72.86	$72.85	$72.90
Purchase #6	$36.94	5.466%	$38.9591	$38.96	$38.95	$39.00
Purchase #7	$62.98	4.352%	$65.7209	$65.72	$65.70	$65.70
7 purchase totals =	$819.89		$894.6812	$894.69	$894.60	$894.80