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	$82.94	8.241%	$89.7751	$89.78	$89.80	$89.80
Purchase #2	$124.72	5.382%	$131.4324	$131.43	$131.45	$131.40
Purchase #3	$198.91	6.615%	$212.0679	$212.07	$212.05	$212.10
Purchase #4	$51.71	4.710%	$54.1455	$54.15	$54.15	$54.10
Purchase #5	$129.58	8.726%	$140.8872	$140.89	$140.90	$140.90
Purchase #6	$81.83	5.614%	$86.4239	$86.42	$86.40	$86.40
Purchase #7	$88.86	12.588%	$100.0457	$100.05	$100.05	$100.00
7 purchase totals =	$758.55		$814.7777	$814.79	$814.80	$814.70