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	$5.57	11.759%	$6.225	$6.23	$6.25	$6.20
Purchase #2	$106.37	6.704%	$113.501	$113.50	$113.50	$113.50
Purchase #3	$100.54	5.800%	$106.3713	$106.37	$106.35	$106.40
Purchase #4	$155.72	12.737%	$175.5541	$175.55	$175.55	$175.60
Purchase #5	$11.40	6.308%	$12.1191	$12.12	$12.10	$12.10
Purchase #6	$231.46	11.694%	$258.5269	$258.53	$258.55	$258.50
Purchase #7	$217.70	5.460%	$229.5864	$229.59	$229.60	$229.60
7 purchase totals =	$828.76		$901.8838	$901.89	$901.90	$901.90