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	$90.63	10.799%	$100.4171	$100.42	$100.40	$100.40
Purchase #2	$50.35	13.166%	$56.9791	$56.98	$57.00	$57.00
Purchase #3	$39.28	3.418%	$40.6226	$40.62	$40.60	$40.60
Purchase #4	$92.60	6.187%	$98.3292	$98.33	$98.35	$98.30
Purchase #5	$157.83	9.832%	$173.3478	$173.35	$173.35	$173.30
Purchase #6	$235.26	6.562%	$250.6978	$250.70	$250.70	$250.70
Purchase #7	$230.66	13.812%	$262.5188	$262.52	$262.50	$262.50
7 purchase totals =	$896.61		$982.9124	$982.92	$982.90	$982.80