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	$11.68	12.346%	$13.122	$13.12	$13.10	$13.10
Purchase #2	$100.44	9.349%	$109.8301	$109.83	$109.85	$109.80
Purchase #3	$126.75	12.289%	$142.3263	$142.33	$142.35	$142.30
Purchase #4	$62.43	8.144%	$67.5143	$67.51	$67.50	$67.50
Purchase #5	$89.30	3.552%	$92.4719	$92.47	$92.45	$92.50
Purchase #6	$187.82	5.271%	$197.72	$197.72	$197.70	$197.70
Purchase #7	$221.75	3.645%	$229.8328	$229.83	$229.85	$229.80
7 purchase totals =	$800.17		$852.8174	$852.81	$852.80	$852.70