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	$136.66	13.671%	$155.3428	$155.34	$155.35	$155.30
Purchase #2	$46.93	7.527%	$50.4624	$50.46	$50.45	$50.50
Purchase #3	$250.92	9.155%	$273.8917	$273.89	$273.90	$273.90
Purchase #4	$37.94	12.333%	$42.6191	$42.62	$42.60	$42.60
Purchase #5	$101.30	5.606%	$106.9789	$106.98	$107.00	$107.00
Purchase #6	$24.58	11.307%	$27.3593	$27.36	$27.35	$27.40
Purchase #7	$48.59	9.238%	$53.0787	$53.08	$53.10	$53.10
7 purchase totals =	$646.92		$709.7329	$709.73	$709.75	$709.80