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	$249.42	9.477%	$273.0575	$273.06	$273.05	$273.10
Purchase #2	$131.61	8.154%	$142.3415	$142.34	$142.35	$142.30
Purchase #3	$235.32	6.465%	$250.5334	$250.53	$250.55	$250.50
Purchase #4	$36.60	6.714%	$39.0573	$39.06	$39.05	$39.10
Purchase #5	$173.52	9.527%	$190.0513	$190.05	$190.05	$190.10
Purchase #6	$234.83	13.133%	$265.6702	$265.67	$265.65	$265.70
Purchase #7	$62.89	3.548%	$65.1213	$65.12	$65.10	$65.10
7 purchase totals =	$1,124.19		$1,225.8325	$1,225.83	$1,225.80	$1,225.90