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	$22.82	6.542%	$24.3129	$24.31	$24.30	$24.30
Purchase #2	$38.82	8.316%	$42.0483	$42.05	$42.05	$42.00
Purchase #3	$138.29	4.404%	$144.3803	$144.38	$144.40	$144.40
Purchase #4	$35.62	5.339%	$37.5218	$37.52	$37.50	$37.50
Purchase #5	$79.48	8.531%	$86.2604	$86.26	$86.25	$86.30
Purchase #6	$86.90	3.649%	$90.071	$90.07	$90.05	$90.10
Purchase #7	$130.64	8.619%	$141.8999	$141.90	$141.90	$141.90
7 purchase totals =	$532.57		$566.4946	$566.49	$566.45	$566.50