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	$15.41	3.111%	$15.8894	$15.89	$15.90	$15.90
Purchase #2	$111.57	11.295%	$124.1718	$124.17	$124.15	$124.20
Purchase #3	$33.51	11.385%	$37.3251	$37.33	$37.35	$37.30
Purchase #4	$107.60	4.854%	$112.8229	$112.82	$112.80	$112.80
Purchase #5	$176.57	12.857%	$199.2716	$199.27	$199.25	$199.30
Purchase #6	$226.46	10.302%	$249.7899	$249.79	$249.80	$249.80
Purchase #7	$92.31	9.699%	$101.2631	$101.26	$101.25	$101.30
7 purchase totals =	$763.43		$840.5338	$840.53	$840.50	$840.60