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	$60.46	6.693%	$64.5066	$64.51	$64.50	$64.50
Purchase #2	$154.45	9.312%	$168.8324	$168.83	$168.85	$168.80
Purchase #3	$167.38	12.675%	$188.5954	$188.60	$188.60	$188.60
Purchase #4	$112.89	5.691%	$119.3146	$119.31	$119.30	$119.30
Purchase #5	$131.47	7.264%	$141.02	$141.02	$141.00	$141.00
Purchase #6	$196.86	9.764%	$216.0814	$216.08	$216.10	$216.10
Purchase #7	$234.88	7.195%	$251.7796	$251.78	$251.80	$251.80
7 purchase totals =	$1,058.39		$1,150.1300	$1,150.13	$1,150.15	$1,150.10