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	$134.70	9.558%	$147.5746	$147.57	$147.55	$147.60
Purchase #2	$103.25	4.160%	$107.5452	$107.55	$107.55	$107.50
Purchase #3	$18.66	6.425%	$19.8589	$19.86	$19.85	$19.90
Purchase #4	$154.27	8.389%	$167.2117	$167.21	$167.20	$167.20
Purchase #5	$89.38	12.162%	$100.2504	$100.25	$100.25	$100.30
Purchase #6	$54.31	12.518%	$61.1085	$61.11	$61.10	$61.10
Purchase #7	$39.43	12.232%	$44.2531	$44.25	$44.25	$44.30
7 purchase totals =	$594.00		$647.8024	$647.80	$647.75	$647.90