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	$55.28	8.228%	$59.8284	$59.83	$59.85	$59.80
Purchase #2	$49.88	4.253%	$52.0014	$52.00	$52.00	$52.00
Purchase #3	$80.84	5.698%	$85.4463	$85.45	$85.45	$85.40
Purchase #4	$42.52	12.598%	$47.8767	$47.88	$47.90	$47.90
Purchase #5	$18.52	13.663%	$21.0504	$21.05	$21.05	$21.10
Purchase #6	$102.91	11.293%	$114.5316	$114.53	$114.55	$114.50
Purchase #7	$136.94	4.778%	$143.483	$143.48	$143.50	$143.50
7 purchase totals =	$486.89		$524.2178	$524.22	$524.30	$524.20