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	$36.83	6.781%	$39.3274	$39.33	$39.35	$39.30
Purchase #2	$132.63	3.589%	$137.3901	$137.39	$137.40	$137.40
Purchase #3	$224.69	6.697%	$239.7375	$239.74	$239.75	$239.70
Purchase #4	$29.83	8.724%	$32.4324	$32.43	$32.45	$32.40
Purchase #5	$69.79	12.390%	$78.437	$78.44	$78.45	$78.40
Purchase #6	$223.42	3.338%	$230.8778	$230.88	$230.90	$230.90
Purchase #7	$35.25	6.154%	$37.4193	$37.42	$37.40	$37.40
7 purchase totals =	$752.44		$795.6215	$795.63	$795.70	$795.50