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	$54.98	4.764%	$57.5992	$57.60	$57.60	$57.60
Purchase #2	$74.80	11.473%	$83.3818	$83.38	$83.40	$83.40
Purchase #3	$19.66	7.574%	$21.149	$21.15	$21.15	$21.10
Purchase #4	$71.44	10.513%	$78.9505	$78.95	$78.95	$79.00
Purchase #5	$198.52	6.224%	$210.8759	$210.88	$210.90	$210.90
Purchase #6	$161.91	3.166%	$167.0361	$167.04	$167.05	$167.00
Purchase #7	$57.82	10.346%	$63.8021	$63.80	$63.80	$63.80
7 purchase totals =	$639.13		$682.7946	$682.80	$682.85	$682.80