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	$77.33	6.529%	$82.3789	$82.38	$82.40	$82.40
Purchase #2	$239.80	6.246%	$254.7779	$254.78	$254.80	$254.80
Purchase #3	$24.73	9.311%	$27.0326	$27.03	$27.05	$27.00
Purchase #4	$97.27	5.804%	$102.9156	$102.92	$102.90	$102.90
Purchase #5	$65.66	9.539%	$71.9233	$71.92	$71.90	$71.90
Purchase #6	$234.62	9.257%	$256.3388	$256.34	$256.35	$256.30
Purchase #7	$40.47	9.274%	$44.2232	$44.22	$44.20	$44.20
7 purchase totals =	$779.88		$839.5903	$839.59	$839.60	$839.50