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	$59.89	3.356%	$61.8999	$61.90	$61.90	$61.90
Purchase #2	$98.66	7.168%	$105.7319	$105.73	$105.75	$105.70
Purchase #3	$8.27	12.286%	$9.2861	$9.29	$9.30	$9.30
Purchase #4	$105.70	13.144%	$119.5932	$119.59	$119.60	$119.60
Purchase #5	$157.97	3.753%	$163.8986	$163.90	$163.90	$163.90
Purchase #6	$37.37	13.490%	$42.4112	$42.41	$42.40	$42.40
Purchase #7	$51.46	10.786%	$57.0105	$57.01	$57.00	$57.00
7 purchase totals =	$519.32		$559.8314	$559.83	$559.85	$559.80