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	$241.38	3.271%	$249.2755	$249.28	$249.30	$249.30
Purchase #2	$55.93	6.428%	$59.5252	$59.53	$59.55	$59.50
Purchase #3	$83.48	3.370%	$86.2933	$86.29	$86.30	$86.30
Purchase #4	$172.61	8.419%	$187.142	$187.14	$187.15	$187.10
Purchase #5	$133.99	8.642%	$145.5694	$145.57	$145.55	$145.60
Purchase #6	$166.64	11.575%	$185.9286	$185.93	$185.95	$185.90
Purchase #7	$245.65	9.776%	$269.6647	$269.66	$269.65	$269.70
7 purchase totals =	$1,099.68		$1,183.3987	$1,183.40	$1,183.45	$1,183.40