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	$136.46	8.522%	$148.0891	$148.09	$148.10	$148.10
Purchase #2	$155.79	6.758%	$166.3183	$166.32	$166.30	$166.30
Purchase #3	$123.96	11.623%	$138.3679	$138.37	$138.35	$138.40
Purchase #4	$131.28	4.140%	$136.715	$136.72	$136.70	$136.70
Purchase #5	$109.56	12.746%	$123.5245	$123.52	$123.50	$123.50
Purchase #6	$129.60	4.666%	$135.6471	$135.65	$135.65	$135.60
Purchase #7	$212.86	11.495%	$237.3283	$237.33	$237.35	$237.30
7 purchase totals =	$999.51		$1,085.9902	$1,086.00	$1,085.95	$1,085.90