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	$88.76	10.652%	$98.2147	$98.21	$98.20	$98.20
Purchase #2	$44.68	12.286%	$50.1694	$50.17	$50.15	$50.20
Purchase #3	$95.53	10.397%	$105.4623	$105.46	$105.45	$105.50
Purchase #4	$61.46	5.329%	$64.7352	$64.74	$64.75	$64.70
Purchase #5	$238.77	13.235%	$270.3712	$270.37	$270.35	$270.40
Purchase #6	$22.39	9.214%	$24.453	$24.45	$24.45	$24.50
Purchase #7	$49.26	9.215%	$53.7993	$53.80	$53.80	$53.80
7 purchase totals =	$600.85		$667.2051	$667.20	$667.15	$667.30