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	$73.87	5.795%	$78.1508	$78.15	$78.15	$78.20
Purchase #2	$250.30	6.788%	$267.2904	$267.29	$267.30	$267.30
Purchase #3	$126.84	13.788%	$144.3287	$144.33	$144.35	$144.30
Purchase #4	$14.47	8.515%	$15.7021	$15.70	$15.70	$15.70
Purchase #5	$67.41	10.681%	$74.6101	$74.61	$74.60	$74.60
Purchase #6	$85.79	10.826%	$95.0776	$95.08	$95.10	$95.10
Purchase #7	$125.72	4.523%	$131.4063	$131.41	$131.40	$131.40
7 purchase totals =	$744.40		$806.5660	$806.57	$806.60	$806.60