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	$66.94	6.443%	$71.2529	$71.25	$71.25	$71.30
Purchase #2	$131.29	7.241%	$140.7967	$140.80	$140.80	$140.80
Purchase #3	$9.51	9.155%	$10.3806	$10.38	$10.40	$10.40
Purchase #4	$49.92	3.445%	$51.6397	$51.64	$51.65	$51.60
Purchase #5	$37.54	11.562%	$41.8804	$41.88	$41.90	$41.90
Purchase #6	$105.69	11.377%	$117.7144	$117.71	$117.70	$117.70
Purchase #7	$107.96	3.658%	$111.9092	$111.91	$111.90	$111.90
7 purchase totals =	$508.85		$545.5739	$545.57	$545.60	$545.60