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	$99.51	12.861%	$112.308	$112.31	$112.30	$112.30
Purchase #2	$98.70	3.838%	$102.4881	$102.49	$102.50	$102.50
Purchase #3	$119.88	3.208%	$123.7258	$123.73	$123.75	$123.70
Purchase #4	$60.27	9.470%	$65.9776	$65.98	$66.00	$66.00
Purchase #5	$201.46	13.870%	$229.4025	$229.40	$229.40	$229.40
Purchase #6	$84.31	9.488%	$92.3093	$92.31	$92.30	$92.30
Purchase #7	$109.75	9.655%	$120.3464	$120.35	$120.35	$120.30
7 purchase totals =	$773.88		$846.5577	$846.57	$846.60	$846.50