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	$70.27	11.387%	$78.2716	$78.27	$78.25	$78.30
Purchase #2	$144.80	9.507%	$158.5661	$158.57	$158.55	$158.60
Purchase #3	$165.47	8.412%	$179.3893	$179.39	$179.40	$179.40
Purchase #4	$78.76	5.595%	$83.1666	$83.17	$83.15	$83.20
Purchase #5	$92.71	6.200%	$98.458	$98.46	$98.45	$98.50
Purchase #6	$7.91	8.556%	$8.5868	$8.59	$8.60	$8.60
Purchase #7	$6.42	8.379%	$6.9579	$6.96	$6.95	$7.00
7 purchase totals =	$566.34		$613.3963	$613.41	$613.35	$613.60