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	$14.54	8.458%	$15.7698	$15.77	$15.75	$15.80
Purchase #2	$150.81	10.180%	$166.1625	$166.16	$166.15	$166.20
Purchase #3	$116.39	10.454%	$128.5574	$128.56	$128.55	$128.60
Purchase #4	$179.95	10.843%	$199.462	$199.46	$199.45	$199.50
Purchase #5	$82.45	8.390%	$89.3676	$89.37	$89.35	$89.40
Purchase #6	$134.52	3.355%	$139.0331	$139.03	$139.05	$139.00
Purchase #7	$98.94	8.654%	$107.5023	$107.50	$107.50	$107.50
7 purchase totals =	$777.60		$845.8547	$845.85	$845.80	$846.00