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	$62.96	5.200%	$66.2339	$66.23	$66.25	$66.20
Purchase #2	$45.88	3.144%	$47.3225	$47.32	$47.30	$47.30
Purchase #3	$58.43	12.855%	$65.9412	$65.94	$65.95	$65.90
Purchase #4	$91.72	5.250%	$96.5353	$96.54	$96.55	$96.50
Purchase #5	$43.72	5.657%	$46.1932	$46.19	$46.20	$46.20
Purchase #6	$183.72	6.854%	$196.3122	$196.31	$196.30	$196.30
Purchase #7	$132.77	11.759%	$148.3824	$148.38	$148.40	$148.40
7 purchase totals =	$619.20		$666.9207	$666.91	$666.95	$666.80