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	$38.54	10.196%	$42.4695	$42.47	$42.45	$42.50
Purchase #2	$131.62	11.743%	$147.0761	$147.08	$147.10	$147.10
Purchase #3	$123.97	13.177%	$140.3055	$140.31	$140.30	$140.30
Purchase #4	$72.97	5.674%	$77.1103	$77.11	$77.10	$77.10
Purchase #5	$111.82	7.187%	$119.8565	$119.86	$119.85	$119.90
Purchase #6	$129.45	8.438%	$140.373	$140.37	$140.35	$140.40
Purchase #7	$69.56	12.146%	$78.0088	$78.01	$78.00	$78.00
7 purchase totals =	$677.93		$745.1997	$745.21	$745.15	$745.30