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	$59.37	13.333%	$67.2858	$67.29	$67.30	$67.30
Purchase #2	$225.32	6.359%	$239.6481	$239.65	$239.65	$239.60
Purchase #3	$35.80	13.111%	$40.4937	$40.49	$40.50	$40.50
Purchase #4	$239.53	13.455%	$271.7588	$271.76	$271.75	$271.80
Purchase #5	$138.84	11.524%	$154.8399	$154.84	$154.85	$154.80
Purchase #6	$87.71	3.479%	$90.7614	$90.76	$90.75	$90.80
Purchase #7	$98.31	6.249%	$104.4534	$104.45	$104.45	$104.50
7 purchase totals =	$884.88		$969.2411	$969.24	$969.25	$969.30