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	$173.89	3.168%	$179.3988	$179.40	$179.40	$179.40
Purchase #2	$166.68	3.245%	$172.0888	$172.09	$172.10	$172.10
Purchase #3	$131.47	6.112%	$139.5054	$139.51	$139.50	$139.50
Purchase #4	$142.57	9.468%	$156.0685	$156.07	$156.05	$156.10
Purchase #5	$32.59	6.595%	$34.7393	$34.74	$34.75	$34.70
Purchase #6	$241.89	3.589%	$250.5714	$250.57	$250.55	$250.60
Purchase #7	$149.94	11.273%	$166.8427	$166.84	$166.85	$166.80
7 purchase totals =	$1,039.03		$1,099.2149	$1,099.22	$1,099.20	$1,099.20