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	$63.30	3.629%	$65.5972	$65.60	$65.60	$65.60
Purchase #2	$206.29	10.773%	$228.5136	$228.51	$228.50	$228.50
Purchase #3	$33.41	13.552%	$37.9377	$37.94	$37.95	$37.90
Purchase #4	$159.39	7.202%	$170.8693	$170.87	$170.85	$170.90
Purchase #5	$87.46	5.761%	$92.4986	$92.50	$92.50	$92.50
Purchase #6	$58.73	6.611%	$62.6126	$62.61	$62.60	$62.60
Purchase #7	$228.91	9.405%	$250.439	$250.44	$250.45	$250.40
7 purchase totals =	$837.49		$908.4680	$908.47	$908.45	$908.40