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	$181.74	3.407%	$187.9319	$187.93	$187.95	$187.90
Purchase #2	$76.51	11.706%	$85.4663	$85.47	$85.45	$85.50
Purchase #3	$136.84	13.676%	$155.5542	$155.55	$155.55	$155.60
Purchase #4	$96.25	12.563%	$108.3419	$108.34	$108.35	$108.30
Purchase #5	$36.28	4.836%	$38.0345	$38.03	$38.05	$38.00
Purchase #6	$151.72	10.625%	$167.8403	$167.84	$167.85	$167.80
Purchase #7	$47.82	10.684%	$52.9291	$52.93	$52.95	$52.90
7 purchase totals =	$727.16		$796.0982	$796.09	$796.15	$796.00