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	$52.57	12.865%	$59.3331	$59.33	$59.35	$59.30
Purchase #2	$118.89	6.501%	$126.619	$126.62	$126.60	$126.60
Purchase #3	$46.68	13.218%	$52.8502	$52.85	$52.85	$52.90
Purchase #4	$83.74	8.282%	$90.6753	$90.68	$90.70	$90.70
Purchase #5	$73.30	11.814%	$81.9597	$81.96	$81.95	$82.00
Purchase #6	$167.88	5.404%	$176.9522	$176.95	$176.95	$177.00
Purchase #7	$85.41	11.747%	$95.4431	$95.44	$95.45	$95.40
7 purchase totals =	$628.47		$683.8326	$683.83	$683.85	$683.90