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	$137.62	13.133%	$155.6936	$155.69	$155.70	$155.70
Purchase #2	$218.42	10.453%	$241.2514	$241.25	$241.25	$241.30
Purchase #3	$97.41	11.129%	$108.2508	$108.25	$108.25	$108.30
Purchase #4	$156.98	6.433%	$167.0785	$167.08	$167.10	$167.10
Purchase #5	$33.91	9.635%	$37.1772	$37.18	$37.20	$37.20
Purchase #6	$24.38	13.682%	$27.7157	$27.72	$27.70	$27.70
Purchase #7	$226.80	6.371%	$241.2494	$241.25	$241.25	$241.20
7 purchase totals =	$895.52		$978.4166	$978.42	$978.45	$978.50