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	$142.96	12.263%	$160.4912	$160.49	$160.50	$160.50
Purchase #2	$238.64	3.107%	$246.0545	$246.05	$246.05	$246.10
Purchase #3	$138.71	5.193%	$145.9132	$145.91	$145.90	$145.90
Purchase #4	$149.34	11.609%	$166.6769	$166.68	$166.70	$166.70
Purchase #5	$18.75	13.522%	$21.2854	$21.29	$21.30	$21.30
Purchase #6	$162.90	10.206%	$179.5256	$179.53	$179.55	$179.50
Purchase #7	$142.57	6.575%	$151.944	$151.94	$151.95	$151.90
7 purchase totals =	$993.87		$1,071.8908	$1,071.89	$1,071.95	$1,071.90