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	$59.78	9.640%	$65.5428	$65.54	$65.55	$65.50
Purchase #2	$43.29	9.532%	$47.4164	$47.42	$47.40	$47.40
Purchase #3	$34.32	10.741%	$38.0063	$38.01	$38.00	$38.00
Purchase #4	$137.96	13.519%	$156.6108	$156.61	$156.60	$156.60
Purchase #5	$124.27	6.410%	$132.2357	$132.24	$132.25	$132.20
Purchase #6	$47.76	12.191%	$53.5824	$53.58	$53.60	$53.60
Purchase #7	$237.31	11.566%	$264.7573	$264.76	$264.75	$264.80
7 purchase totals =	$684.69		$758.1517	$758.16	$758.15	$758.10