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	$167.85	12.197%	$188.3227	$188.32	$188.30	$188.30
Purchase #2	$178.99	3.795%	$185.7827	$185.78	$185.80	$185.80
Purchase #3	$125.57	9.473%	$137.4652	$137.47	$137.45	$137.50
Purchase #4	$100.68	3.823%	$104.529	$104.53	$104.55	$104.50
Purchase #5	$115.78	12.504%	$130.2571	$130.26	$130.25	$130.30
Purchase #6	$235.93	12.509%	$265.4425	$265.44	$265.45	$265.40
Purchase #7	$198.52	6.794%	$212.0074	$212.01	$212.00	$212.00
7 purchase totals =	$1,123.32		$1,223.8066	$1,223.81	$1,223.80	$1,223.80