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	$102.47	8.719%	$111.4044	$111.40	$111.40	$111.40
Purchase #2	$132.61	11.239%	$147.514	$147.51	$147.50	$147.50
Purchase #3	$25.87	4.695%	$27.0846	$27.08	$27.10	$27.10
Purchase #4	$130.47	7.818%	$140.6701	$140.67	$140.65	$140.70
Purchase #5	$171.64	10.426%	$189.5352	$189.54	$189.55	$189.50
Purchase #6	$198.97	12.526%	$223.893	$223.89	$223.90	$223.90
Purchase #7	$72.42	10.701%	$80.1697	$80.17	$80.15	$80.20
7 purchase totals =	$834.45		$920.2710	$920.26	$920.25	$920.30