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	$210.51	13.269%	$238.4426	$238.44	$238.45	$238.40
Purchase #2	$89.29	3.598%	$92.5027	$92.50	$92.50	$92.50
Purchase #3	$165.71	8.520%	$179.8285	$179.83	$179.85	$179.80
Purchase #4	$179.85	6.251%	$191.0924	$191.09	$191.10	$191.10
Purchase #5	$111.57	9.843%	$122.5518	$122.55	$122.55	$122.60
Purchase #6	$70.79	12.397%	$79.5658	$79.57	$79.55	$79.60
Purchase #7	$107.63	8.322%	$116.587	$116.59	$116.60	$116.60
7 purchase totals =	$935.35		$1,020.5708	$1,020.57	$1,020.60	$1,020.60