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	$97.32	7.300%	$104.4244	$104.42	$104.40	$104.40
Purchase #2	$99.53	9.748%	$109.2322	$109.23	$109.25	$109.20
Purchase #3	$48.70	5.847%	$51.5475	$51.55	$51.55	$51.50
Purchase #4	$197.39	12.638%	$222.3361	$222.34	$222.35	$222.30
Purchase #5	$49.57	3.703%	$51.4056	$51.41	$51.40	$51.40
Purchase #6	$242.79	8.113%	$262.4876	$262.49	$262.50	$262.50
Purchase #7	$74.78	11.138%	$83.109	$83.11	$83.10	$83.10
7 purchase totals =	$810.08		$884.5424	$884.55	$884.55	$884.40