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	$247.99	6.822%	$264.9079	$264.91	$264.90	$264.90
Purchase #2	$177.83	7.168%	$190.5769	$190.58	$190.60	$190.60
Purchase #3	$29.79	10.464%	$32.9072	$32.91	$32.90	$32.90
Purchase #4	$32.64	7.741%	$35.1667	$35.17	$35.15	$35.20
Purchase #5	$162.95	13.838%	$185.499	$185.50	$185.50	$185.50
Purchase #6	$210.76	8.768%	$229.2394	$229.24	$229.25	$229.20
Purchase #7	$237.89	9.506%	$260.5038	$260.50	$260.50	$260.50
7 purchase totals =	$1,099.85		$1,198.8009	$1,198.81	$1,198.80	$1,198.80