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	$72.59	5.397%	$76.5077	$76.51	$76.50	$76.50
Purchase #2	$33.63	10.600%	$37.1948	$37.19	$37.20	$37.20
Purchase #3	$35.76	5.243%	$37.6349	$37.63	$37.65	$37.60
Purchase #4	$201.62	12.303%	$226.4253	$226.43	$226.45	$226.40
Purchase #5	$10.54	9.854%	$11.5786	$11.58	$11.60	$11.60
Purchase #6	$103.39	12.441%	$116.2527	$116.25	$116.25	$116.30
Purchase #7	$72.79	8.320%	$78.8461	$78.85	$78.85	$78.80
7 purchase totals =	$530.32		$584.4401	$584.44	$584.50	$584.40