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	$166.93	13.677%	$189.761	$189.76	$189.75	$189.80
Purchase #2	$180.25	8.307%	$195.2234	$195.22	$195.20	$195.20
Purchase #3	$198.43	8.616%	$215.5267	$215.53	$215.55	$215.50
Purchase #4	$250.66	13.517%	$284.5417	$284.54	$284.55	$284.50
Purchase #5	$67.97	5.773%	$71.8939	$71.89	$71.90	$71.90
Purchase #6	$156.46	10.105%	$172.2703	$172.27	$172.25	$172.30
Purchase #7	$176.95	4.136%	$184.2687	$184.27	$184.25	$184.30
7 purchase totals =	$1,197.65		$1,313.4857	$1,313.48	$1,313.45	$1,313.50