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	$37.58	3.357%	$38.8416	$38.84	$38.85	$38.80
Purchase #2	$246.59	10.664%	$272.8864	$272.89	$272.90	$272.90
Purchase #3	$19.43	6.379%	$20.6694	$20.67	$20.65	$20.70
Purchase #4	$239.85	4.435%	$250.4873	$250.49	$250.50	$250.50
Purchase #5	$122.95	9.452%	$134.5712	$134.57	$134.55	$134.60
Purchase #6	$99.43	5.123%	$104.5238	$104.52	$104.50	$104.50
Purchase #7	$72.34	10.801%	$80.1534	$80.15	$80.15	$80.20
7 purchase totals =	$838.17		$902.1331	$902.13	$902.10	$902.20