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	$239.33	3.627%	$248.0105	$248.01	$248.00	$248.00
Purchase #2	$105.41	5.511%	$111.2191	$111.22	$111.20	$111.20
Purchase #3	$15.60	5.790%	$16.5032	$16.50	$16.50	$16.50
Purchase #4	$97.31	12.562%	$109.5341	$109.53	$109.55	$109.50
Purchase #5	$22.76	3.598%	$23.5789	$23.58	$23.60	$23.60
Purchase #6	$157.84	6.844%	$168.6426	$168.64	$168.65	$168.60
Purchase #7	$141.97	8.406%	$153.904	$153.90	$153.90	$153.90
7 purchase totals =	$780.22		$831.3924	$831.38	$831.40	$831.30