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	$211.85	13.654%	$240.776	$240.78	$240.80	$240.80
Purchase #2	$171.70	11.435%	$191.3339	$191.33	$191.35	$191.30
Purchase #3	$110.60	5.631%	$116.8279	$116.83	$116.85	$116.80
Purchase #4	$75.37	4.671%	$78.8905	$78.89	$78.90	$78.90
Purchase #5	$123.88	7.764%	$133.498	$133.50	$133.50	$133.50
Purchase #6	$151.52	4.681%	$158.6127	$158.61	$158.60	$158.60
Purchase #7	$19.68	4.289%	$20.5241	$20.52	$20.50	$20.50
7 purchase totals =	$864.60		$940.4631	$940.46	$940.50	$940.40