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	$234.68	10.469%	$259.2486	$259.25	$259.25	$259.20
Purchase #2	$59.60	5.417%	$62.8285	$62.83	$62.85	$62.80
Purchase #3	$15.60	11.268%	$17.3578	$17.36	$17.35	$17.40
Purchase #4	$70.46	13.833%	$80.2067	$80.21	$80.20	$80.20
Purchase #5	$191.35	4.872%	$200.6726	$200.67	$200.65	$200.70
Purchase #6	$105.43	3.759%	$109.3931	$109.39	$109.40	$109.40
Purchase #7	$48.54	11.670%	$54.2046	$54.20	$54.20	$54.20
7 purchase totals =	$725.66		$783.9119	$783.91	$783.90	$783.90