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	$86.95	4.404%	$90.7793	$90.78	$90.80	$90.80
Purchase #2	$176.77	12.552%	$198.9582	$198.96	$198.95	$199.00
Purchase #3	$57.29	4.279%	$59.7414	$59.74	$59.75	$59.70
Purchase #4	$50.83	3.747%	$52.7346	$52.73	$52.75	$52.70
Purchase #5	$31.99	7.661%	$34.4408	$34.44	$34.45	$34.40
Purchase #6	$185.51	4.241%	$193.3775	$193.38	$193.40	$193.40
Purchase #7	$46.48	9.855%	$51.0606	$51.06	$51.05	$51.10
7 purchase totals =	$635.82		$681.0924	$681.09	$681.15	$681.10