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	$38.25	11.595%	$42.6851	$42.69	$42.70	$42.70
Purchase #2	$83.37	8.472%	$90.4331	$90.43	$90.45	$90.40
Purchase #3	$187.25	12.358%	$210.3904	$210.39	$210.40	$210.40
Purchase #4	$99.31	10.703%	$109.9391	$109.94	$109.95	$109.90
Purchase #5	$59.92	6.522%	$63.828	$63.83	$63.85	$63.80
Purchase #6	$188.47	10.769%	$208.7663	$208.77	$208.75	$208.80
Purchase #7	$134.85	9.771%	$148.0262	$148.03	$148.05	$148.00
7 purchase totals =	$791.42		$874.0682	$874.08	$874.15	$874.00