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	$5.37	13.418%	$6.0905	$6.09	$6.10	$6.10
Purchase #2	$232.39	12.330%	$261.0437	$261.04	$261.05	$261.00
Purchase #3	$107.39	11.490%	$119.7291	$119.73	$119.75	$119.70
Purchase #4	$56.56	8.695%	$61.4779	$61.48	$61.50	$61.50
Purchase #5	$126.60	11.734%	$141.4552	$141.46	$141.45	$141.50
Purchase #6	$151.72	7.172%	$162.6014	$162.60	$162.60	$162.60
Purchase #7	$100.27	5.667%	$105.9523	$105.95	$105.95	$106.00
7 purchase totals =	$780.30		$858.3501	$858.35	$858.40	$858.40