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	$38.77	13.265%	$43.9128	$43.91	$43.90	$43.90
Purchase #2	$155.31	10.197%	$171.147	$171.15	$171.15	$171.10
Purchase #3	$126.32	8.687%	$137.2934	$137.29	$137.30	$137.30
Purchase #4	$53.50	11.302%	$59.5466	$59.55	$59.55	$59.50
Purchase #5	$70.85	7.808%	$76.382	$76.38	$76.40	$76.40
Purchase #6	$87.38	12.197%	$98.0377	$98.04	$98.05	$98.00
Purchase #7	$40.93	5.336%	$43.114	$43.11	$43.10	$43.10
7 purchase totals =	$573.06		$629.4335	$629.43	$629.45	$629.30