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	$22.48	8.483%	$24.387	$24.39	$24.40	$24.40
Purchase #2	$65.68	10.637%	$72.6664	$72.67	$72.65	$72.70
Purchase #3	$5.70	3.614%	$5.906	$5.91	$5.90	$5.90
Purchase #4	$111.66	13.757%	$127.0211	$127.02	$127.00	$127.00
Purchase #5	$37.54	10.761%	$41.5797	$41.58	$41.60	$41.60
Purchase #6	$90.90	4.208%	$94.7251	$94.73	$94.75	$94.70
Purchase #7	$150.44	13.831%	$171.2474	$171.25	$171.25	$171.20
7 purchase totals =	$484.40		$537.5327	$537.55	$537.55	$537.50