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	$182.99	3.806%	$189.9546	$189.95	$189.95	$190.00
Purchase #2	$92.84	13.541%	$105.4115	$105.41	$105.40	$105.40
Purchase #3	$94.45	3.153%	$97.428	$97.43	$97.45	$97.40
Purchase #4	$249.80	3.430%	$258.3681	$258.37	$258.35	$258.40
Purchase #5	$12.61	10.323%	$13.9117	$13.91	$13.90	$13.90
Purchase #6	$88.54	12.425%	$99.5411	$99.54	$99.55	$99.50
Purchase #7	$74.65	5.565%	$78.8043	$78.80	$78.80	$78.80
7 purchase totals =	$795.88		$843.4193	$843.41	$843.40	$843.40