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	$79.99	12.465%	$89.9608	$89.96	$89.95	$90.00
Purchase #2	$213.43	5.105%	$224.3256	$224.33	$224.35	$224.30
Purchase #3	$96.89	9.112%	$105.7186	$105.72	$105.70	$105.70
Purchase #4	$47.86	7.834%	$51.6094	$51.61	$51.60	$51.60
Purchase #5	$153.41	9.331%	$167.7247	$167.72	$167.70	$167.70
Purchase #6	$153.59	9.268%	$167.8247	$167.82	$167.80	$167.80
Purchase #7	$151.88	13.849%	$172.9139	$172.91	$172.90	$172.90
7 purchase totals =	$897.05		$980.0777	$980.07	$980.00	$980.00