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	$169.78	8.153%	$183.6222	$183.62	$183.60	$183.60
Purchase #2	$250.32	9.756%	$274.7412	$274.74	$274.75	$274.70
Purchase #3	$117.28	5.322%	$123.5216	$123.52	$123.50	$123.50
Purchase #4	$235.45	13.470%	$267.1651	$267.17	$267.15	$267.20
Purchase #5	$73.96	6.716%	$78.9272	$78.93	$78.95	$78.90
Purchase #6	$107.64	11.214%	$119.7107	$119.71	$119.70	$119.70
Purchase #7	$33.47	13.488%	$37.9844	$37.98	$38.00	$38.00
7 purchase totals =	$987.90		$1,085.6724	$1,085.67	$1,085.65	$1,085.60