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	$116.25	3.728%	$120.5838	$120.58	$120.60	$120.60
Purchase #2	$167.59	5.323%	$176.5108	$176.51	$176.50	$176.50
Purchase #3	$130.26	13.235%	$147.4999	$147.50	$147.50	$147.50
Purchase #4	$14.90	6.147%	$15.8159	$15.82	$15.80	$15.80
Purchase #5	$137.90	10.600%	$152.5174	$152.52	$152.50	$152.50
Purchase #6	$71.85	9.828%	$78.9114	$78.91	$78.90	$78.90
Purchase #7	$119.46	8.706%	$129.8602	$129.86	$129.85	$129.90
7 purchase totals =	$758.21		$821.6994	$821.70	$821.65	$821.70