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	$150.31	9.227%	$164.1791	$164.18	$164.20	$164.20
Purchase #2	$158.96	11.671%	$177.5122	$177.51	$177.50	$177.50
Purchase #3	$93.86	6.487%	$99.9487	$99.95	$99.95	$99.90
Purchase #4	$130.41	5.410%	$137.4652	$137.47	$137.45	$137.50
Purchase #5	$112.79	4.857%	$118.2682	$118.27	$118.25	$118.30
Purchase #6	$202.95	4.181%	$211.4353	$211.44	$211.45	$211.40
Purchase #7	$229.59	11.639%	$256.312	$256.31	$256.30	$256.30
7 purchase totals =	$1,078.87		$1,165.1207	$1,165.13	$1,165.10	$1,165.10