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	$65.71	7.288%	$70.4989	$70.50	$70.50	$70.50
Purchase #2	$123.86	11.496%	$138.0989	$138.10	$138.10	$138.10
Purchase #3	$106.29	6.767%	$113.4826	$113.48	$113.50	$113.50
Purchase #4	$223.50	3.598%	$231.5415	$231.54	$231.55	$231.50
Purchase #5	$172.93	10.449%	$190.9995	$191.00	$191.00	$191.00
Purchase #6	$37.46	10.158%	$41.2652	$41.27	$41.25	$41.30
Purchase #7	$188.32	5.222%	$198.1541	$198.15	$198.15	$198.20
7 purchase totals =	$918.07		$984.0407	$984.04	$984.05	$984.10