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	$35.45	6.285%	$37.678	$37.68	$37.70	$37.70
Purchase #2	$198.59	8.427%	$215.3252	$215.33	$215.35	$215.30
Purchase #3	$225.38	3.845%	$234.0459	$234.05	$234.05	$234.00
Purchase #4	$34.46	12.547%	$38.7837	$38.78	$38.80	$38.80
Purchase #5	$67.47	8.292%	$73.0646	$73.06	$73.05	$73.10
Purchase #6	$111.89	7.660%	$120.4608	$120.46	$120.45	$120.50
Purchase #7	$54.39	12.316%	$61.0887	$61.09	$61.10	$61.10
7 purchase totals =	$727.63		$780.4469	$780.45	$780.50	$780.50