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	$227.98	9.407%	$249.4261	$249.43	$249.45	$249.40
Purchase #2	$183.50	3.246%	$189.4564	$189.46	$189.45	$189.50
Purchase #3	$133.89	5.544%	$141.3129	$141.31	$141.30	$141.30
Purchase #4	$45.95	6.743%	$49.0484	$49.05	$49.05	$49.00
Purchase #5	$242.35	7.619%	$260.8146	$260.81	$260.80	$260.80
Purchase #6	$53.65	11.425%	$59.7795	$59.78	$59.80	$59.80
Purchase #7	$87.70	3.135%	$90.4494	$90.45	$90.45	$90.40
7 purchase totals =	$975.02		$1,040.2873	$1,040.29	$1,040.30	$1,040.20