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	$173.95	10.147%	$191.6007	$191.60	$191.60	$191.60
Purchase #2	$95.72	3.455%	$99.0271	$99.03	$99.05	$99.00
Purchase #3	$44.50	7.229%	$47.7169	$47.72	$47.70	$47.70
Purchase #4	$60.68	11.663%	$67.7571	$67.76	$67.75	$67.80
Purchase #5	$6.93	12.591%	$7.8026	$7.80	$7.80	$7.80
Purchase #6	$114.95	3.852%	$119.3779	$119.38	$119.40	$119.40
Purchase #7	$34.82	10.790%	$38.5771	$38.58	$38.60	$38.60
7 purchase totals =	$531.55		$571.8594	$571.87	$571.90	$571.90