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	$204.89	8.674%	$222.6622	$222.66	$222.65	$222.70
Purchase #2	$243.46	7.653%	$262.092	$262.09	$262.10	$262.10
Purchase #3	$170.32	4.336%	$177.7051	$177.71	$177.70	$177.70
Purchase #4	$43.85	3.585%	$45.422	$45.42	$45.40	$45.40
Purchase #5	$106.29	3.527%	$110.0388	$110.04	$110.05	$110.00
Purchase #6	$63.74	12.789%	$71.8917	$71.89	$71.90	$71.90
Purchase #7	$38.48	4.118%	$40.0646	$40.06	$40.05	$40.10
7 purchase totals =	$871.03		$929.8764	$929.87	$929.85	$929.90