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	$75.74	13.772%	$86.1709	$86.17	$86.15	$86.20
Purchase #2	$89.85	12.366%	$100.9609	$100.96	$100.95	$101.00
Purchase #3	$86.34	10.561%	$95.4584	$95.46	$95.45	$95.50
Purchase #4	$112.33	12.812%	$126.7217	$126.72	$126.70	$126.70
Purchase #5	$11.56	7.726%	$12.4531	$12.45	$12.45	$12.50
Purchase #6	$124.44	12.439%	$139.9191	$139.92	$139.90	$139.90
Purchase #7	$192.85	11.796%	$215.5986	$215.60	$215.60	$215.60
7 purchase totals =	$693.11		$777.2827	$777.28	$777.20	$777.40