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	$29.31	7.296%	$31.4485	$31.45	$31.45	$31.40
Purchase #2	$184.85	11.615%	$206.3203	$206.32	$206.30	$206.30
Purchase #3	$65.82	9.403%	$72.0091	$72.01	$72.00	$72.00
Purchase #4	$52.75	4.328%	$55.033	$55.03	$55.05	$55.00
Purchase #5	$128.97	10.530%	$142.5505	$142.55	$142.55	$142.60
Purchase #6	$55.30	12.284%	$62.0931	$62.09	$62.10	$62.10
Purchase #7	$53.99	10.511%	$59.6649	$59.66	$59.65	$59.70
7 purchase totals =	$570.99		$629.1194	$629.11	$629.10	$629.10