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	$166.27	13.553%	$188.8046	$188.80	$188.80	$188.80
Purchase #2	$188.70	12.705%	$212.6743	$212.67	$212.65	$212.70
Purchase #3	$78.47	9.413%	$85.8564	$85.86	$85.85	$85.90
Purchase #4	$39.72	9.766%	$43.5991	$43.60	$43.60	$43.60
Purchase #5	$17.57	9.187%	$19.1842	$19.18	$19.20	$19.20
Purchase #6	$246.85	11.728%	$275.8006	$275.80	$275.80	$275.80
Purchase #7	$30.64	10.336%	$33.807	$33.81	$33.80	$33.80
7 purchase totals =	$768.22		$859.7262	$859.72	$859.70	$859.80