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	$68.50	5.124%	$72.0099	$72.01	$72.00	$72.00
Purchase #2	$144.85	9.709%	$158.9135	$158.91	$158.90	$158.90
Purchase #3	$84.35	6.291%	$89.6565	$89.66	$89.65	$89.70
Purchase #4	$139.99	11.732%	$156.4136	$156.41	$156.40	$156.40
Purchase #5	$189.59	3.381%	$196	$196.00	$196.00	$196.00
Purchase #6	$160.95	3.602%	$166.7474	$166.75	$166.75	$166.70
Purchase #7	$52.98	12.233%	$59.461	$59.46	$59.45	$59.50
7 purchase totals =	$841.21		$899.2019	$899.20	$899.15	$899.20