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	$64.46	11.817%	$72.0772	$72.08	$72.10	$72.10
Purchase #2	$207.87	7.371%	$223.1921	$223.19	$223.20	$223.20
Purchase #3	$106.46	5.484%	$112.2983	$112.30	$112.30	$112.30
Purchase #4	$65.46	9.546%	$71.7088	$71.71	$71.70	$71.70
Purchase #5	$193.96	13.663%	$220.4608	$220.46	$220.45	$220.50
Purchase #6	$56.35	8.514%	$61.1476	$61.15	$61.15	$61.10
Purchase #7	$242.25	5.672%	$255.9904	$255.99	$256.00	$256.00
7 purchase totals =	$936.81		$1,016.8752	$1,016.88	$1,016.90	$1,016.90