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	$72.55	8.177%	$78.4824	$78.48	$78.50	$78.50
Purchase #2	$227.65	10.267%	$251.0228	$251.02	$251.00	$251.00
Purchase #3	$84.29	6.571%	$89.8287	$89.83	$89.85	$89.80
Purchase #4	$226.74	4.790%	$237.6008	$237.60	$237.60	$237.60
Purchase #5	$70.61	10.354%	$77.921	$77.92	$77.90	$77.90
Purchase #6	$77.45	11.826%	$86.6092	$86.61	$86.60	$86.60
Purchase #7	$131.79	11.398%	$146.8114	$146.81	$146.80	$146.80
7 purchase totals =	$891.08		$968.2763	$968.27	$968.25	$968.20