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	$109.34	8.149%	$118.2501	$118.25	$118.25	$118.30
Purchase #2	$43.54	13.766%	$49.5337	$49.53	$49.55	$49.50
Purchase #3	$146.54	8.150%	$158.483	$158.48	$158.50	$158.50
Purchase #4	$14.97	3.572%	$15.5047	$15.50	$15.50	$15.50
Purchase #5	$53.25	12.588%	$59.9531	$59.95	$59.95	$60.00
Purchase #6	$158.38	12.401%	$178.0207	$178.02	$178.00	$178.00
Purchase #7	$80.77	6.737%	$86.2115	$86.21	$86.20	$86.20
7 purchase totals =	$606.79		$665.9568	$665.94	$665.95	$666.00