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	$118.90	6.197%	$126.2682	$126.27	$126.25	$126.30
Purchase #2	$141.96	6.117%	$150.6437	$150.64	$150.65	$150.60
Purchase #3	$5.82	10.145%	$6.4104	$6.41	$6.40	$6.40
Purchase #4	$174.33	9.137%	$190.2585	$190.26	$190.25	$190.30
Purchase #5	$107.76	9.574%	$118.0769	$118.08	$118.10	$118.10
Purchase #6	$202.27	6.647%	$215.7149	$215.71	$215.70	$215.70
Purchase #7	$79.85	7.119%	$85.5345	$85.53	$85.55	$85.50
7 purchase totals =	$830.89		$892.9071	$892.90	$892.90	$892.90