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	$45.40	13.497%	$51.5276	$51.53	$51.55	$51.50
Purchase #2	$166.88	7.349%	$179.144	$179.14	$179.15	$179.10
Purchase #3	$185.67	12.703%	$209.2557	$209.26	$209.25	$209.30
Purchase #4	$149.65	11.599%	$167.0079	$167.01	$167.00	$167.00
Purchase #5	$126.75	10.134%	$139.5948	$139.59	$139.60	$139.60
Purchase #6	$61.82	6.814%	$66.0324	$66.03	$66.05	$66.00
Purchase #7	$146.44	6.618%	$156.1314	$156.13	$156.15	$156.10
7 purchase totals =	$882.61		$968.6938	$968.69	$968.75	$968.60