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	$57.93	9.104%	$63.2039	$63.20	$63.20	$63.20
Purchase #2	$54.42	12.660%	$61.3096	$61.31	$61.30	$61.30
Purchase #3	$172.49	13.783%	$196.2643	$196.26	$196.25	$196.30
Purchase #4	$37.79	6.134%	$40.108	$40.11	$40.10	$40.10
Purchase #5	$75.79	3.119%	$78.1539	$78.15	$78.15	$78.20
Purchase #6	$76.64	4.698%	$80.2405	$80.24	$80.25	$80.20
Purchase #7	$220.78	8.289%	$239.0805	$239.08	$239.10	$239.10
7 purchase totals =	$695.84		$758.3607	$758.35	$758.35	$758.40