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	$70.93	10.499%	$78.3769	$78.38	$78.40	$78.40
Purchase #2	$168.32	8.489%	$182.6087	$182.61	$182.60	$182.60
Purchase #3	$240.73	11.850%	$269.2565	$269.26	$269.25	$269.30
Purchase #4	$9.37	12.231%	$10.516	$10.52	$10.50	$10.50
Purchase #5	$91.62	11.545%	$102.1975	$102.20	$102.20	$102.20
Purchase #6	$38.45	6.150%	$40.8147	$40.81	$40.80	$40.80
Purchase #7	$123.33	7.732%	$132.8659	$132.87	$132.85	$132.90
7 purchase totals =	$742.75		$816.6362	$816.65	$816.60	$816.70