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	$120.43	11.786%	$134.6239	$134.62	$134.60	$134.60
Purchase #2	$95.94	13.570%	$108.9591	$108.96	$108.95	$109.00
Purchase #3	$35.90	4.421%	$37.4871	$37.49	$37.50	$37.50
Purchase #4	$11.88	10.804%	$13.1635	$13.16	$13.15	$13.20
Purchase #5	$121.72	10.175%	$134.105	$134.11	$134.10	$134.10
Purchase #6	$19.25	13.311%	$21.8124	$21.81	$21.80	$21.80
Purchase #7	$46.55	11.501%	$51.9037	$51.90	$51.90	$51.90
7 purchase totals =	$451.67		$502.0547	$502.05	$502.00	$502.10