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	$171.44	3.728%	$177.8313	$177.83	$177.85	$177.80
Purchase #2	$30.39	6.320%	$32.3106	$32.31	$32.30	$32.30
Purchase #3	$128.79	5.501%	$135.8747	$135.87	$135.85	$135.90
Purchase #4	$126.60	12.525%	$142.4567	$142.46	$142.45	$142.50
Purchase #5	$196.94	11.654%	$219.8914	$219.89	$219.90	$219.90
Purchase #6	$128.72	8.724%	$139.9495	$139.95	$139.95	$139.90
Purchase #7	$109.72	12.106%	$123.0027	$123.00	$123.00	$123.00
7 purchase totals =	$892.60		$971.3169	$971.31	$971.30	$971.30