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	$45.98	12.790%	$51.8608	$51.86	$51.85	$51.90
Purchase #2	$178.99	7.168%	$191.82	$191.82	$191.80	$191.80
Purchase #3	$52.50	7.322%	$56.3441	$56.34	$56.35	$56.30
Purchase #4	$29.84	13.338%	$33.8201	$33.82	$33.80	$33.80
Purchase #5	$173.51	3.395%	$179.4007	$179.40	$179.40	$179.40
Purchase #6	$137.26	10.181%	$151.2344	$151.23	$151.25	$151.20
Purchase #7	$22.31	4.818%	$23.3849	$23.38	$23.40	$23.40
7 purchase totals =	$640.39		$687.8650	$687.85	$687.85	$687.80