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	$189.34	5.856%	$200.4278	$200.43	$200.45	$200.40
Purchase #2	$103.72	11.315%	$115.4559	$115.46	$115.45	$115.50
Purchase #3	$92.93	4.206%	$96.8386	$96.84	$96.85	$96.80
Purchase #4	$11.41	9.571%	$12.5021	$12.50	$12.50	$12.50
Purchase #5	$75.61	12.271%	$84.8881	$84.89	$84.90	$84.90
Purchase #6	$230.66	3.256%	$238.1703	$238.17	$238.15	$238.20
Purchase #7	$229.27	9.611%	$251.3051	$251.31	$251.30	$251.30
7 purchase totals =	$932.94		$999.5879	$999.60	$999.60	$999.60