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	$131.25	9.251%	$143.3919	$143.39	$143.40	$143.40
Purchase #2	$29.90	5.649%	$31.5891	$31.59	$31.60	$31.60
Purchase #3	$227.38	12.746%	$256.3619	$256.36	$256.35	$256.40
Purchase #4	$168.41	7.161%	$180.4698	$180.47	$180.45	$180.50
Purchase #5	$42.58	7.139%	$45.6198	$45.62	$45.60	$45.60
Purchase #6	$132.29	11.651%	$147.7031	$147.70	$147.70	$147.70
Purchase #7	$172.36	12.149%	$193.3	$193.30	$193.30	$193.30
7 purchase totals =	$904.17		$998.4356	$998.43	$998.40	$998.50