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	$150.61	10.259%	$166.0611	$166.06	$166.05	$166.10
Purchase #2	$32.76	13.340%	$37.1302	$37.13	$37.15	$37.10
Purchase #3	$237.27	11.863%	$265.4173	$265.42	$265.40	$265.40
Purchase #4	$160.86	10.190%	$177.2516	$177.25	$177.25	$177.30
Purchase #5	$44.80	8.612%	$48.6582	$48.66	$48.65	$48.70
Purchase #6	$79.34	6.164%	$84.2305	$84.23	$84.25	$84.20
Purchase #7	$227.85	4.505%	$238.1146	$238.11	$238.10	$238.10
7 purchase totals =	$933.49		$1,016.8635	$1,016.86	$1,016.85	$1,016.90