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	$75.96	5.512%	$80.1469	$80.15	$80.15	$80.10
Purchase #2	$83.48	3.205%	$86.1555	$86.16	$86.15	$86.20
Purchase #3	$103.35	4.447%	$107.946	$107.95	$107.95	$107.90
Purchase #4	$92.86	12.847%	$104.7897	$104.79	$104.80	$104.80
Purchase #5	$149.54	7.108%	$160.1693	$160.17	$160.15	$160.20
Purchase #6	$63.86	13.243%	$72.317	$72.32	$72.30	$72.30
Purchase #7	$33.43	13.131%	$37.8197	$37.82	$37.80	$37.80
7 purchase totals =	$602.48		$649.3441	$649.36	$649.30	$649.30