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	$117.51	11.582%	$131.12	$131.12	$131.10	$131.10
Purchase #2	$76.68	5.288%	$80.7348	$80.73	$80.75	$80.70
Purchase #3	$52.52	9.264%	$57.3855	$57.39	$57.40	$57.40
Purchase #4	$43.28	10.520%	$47.8331	$47.83	$47.85	$47.80
Purchase #5	$46.48	6.416%	$49.4622	$49.46	$49.45	$49.50
Purchase #6	$150.45	4.235%	$156.8216	$156.82	$156.80	$156.80
Purchase #7	$59.33	12.493%	$66.7421	$66.74	$66.75	$66.70
7 purchase totals =	$546.25		$590.0993	$590.09	$590.10	$590.00