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	$224.81	6.352%	$239.0899	$239.09	$239.10	$239.10
Purchase #2	$242.56	5.618%	$256.187	$256.19	$256.20	$256.20
Purchase #3	$81.56	10.282%	$89.946	$89.95	$89.95	$89.90
Purchase #4	$43.31	4.285%	$45.1658	$45.17	$45.15	$45.20
Purchase #5	$134.59	6.635%	$143.52	$143.52	$143.50	$143.50
Purchase #6	$198.89	3.548%	$205.9466	$205.95	$205.95	$205.90
Purchase #7	$194.93	8.804%	$212.0916	$212.09	$212.10	$212.10
7 purchase totals =	$1,120.65		$1,191.9469	$1,191.96	$1,191.95	$1,191.90