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	$223.33	11.417%	$248.8276	$248.83	$248.85	$248.80
Purchase #2	$87.68	6.602%	$93.4686	$93.47	$93.45	$93.50
Purchase #3	$71.35	10.213%	$78.637	$78.64	$78.65	$78.60
Purchase #4	$100.88	3.481%	$104.3916	$104.39	$104.40	$104.40
Purchase #5	$28.40	3.408%	$29.3679	$29.37	$29.35	$29.40
Purchase #6	$90.38	11.281%	$100.5758	$100.58	$100.60	$100.60
Purchase #7	$141.48	9.533%	$154.9673	$154.97	$154.95	$155.00
7 purchase totals =	$743.50		$810.2358	$810.25	$810.25	$810.30