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	$103.79	13.604%	$117.9096	$117.91	$117.90	$117.90
Purchase #2	$25.55	6.358%	$27.1745	$27.17	$27.15	$27.20
Purchase #3	$147.45	5.617%	$155.7323	$155.73	$155.75	$155.70
Purchase #4	$35.60	12.499%	$40.0496	$40.05	$40.05	$40.00
Purchase #5	$113.34	12.317%	$127.3001	$127.30	$127.30	$127.30
Purchase #6	$214.78	4.231%	$223.8673	$223.87	$223.85	$223.90
Purchase #7	$220.49	8.634%	$239.5271	$239.53	$239.55	$239.50
7 purchase totals =	$861.00		$931.5605	$931.56	$931.55	$931.50