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	$29.59	7.763%	$31.8871	$31.89	$31.90	$31.90
Purchase #2	$51.76	9.187%	$56.5152	$56.52	$56.50	$56.50
Purchase #3	$148.97	10.712%	$164.9277	$164.93	$164.95	$164.90
Purchase #4	$160.98	3.624%	$166.8139	$166.81	$166.80	$166.80
Purchase #5	$63.53	5.518%	$67.0356	$67.04	$67.05	$67.00
Purchase #6	$57.56	12.119%	$64.5357	$64.54	$64.55	$64.50
Purchase #7	$18.34	7.420%	$19.7008	$19.70	$19.70	$19.70
7 purchase totals =	$530.73		$571.4160	$571.43	$571.45	$571.30