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	$180.81	13.260%	$204.7854	$204.79	$204.80	$204.80
Purchase #2	$46.76	9.239%	$51.0802	$51.08	$51.10	$51.10
Purchase #3	$38.46	11.331%	$42.8179	$42.82	$42.80	$42.80
Purchase #4	$64.82	4.328%	$67.6254	$67.63	$67.65	$67.60
Purchase #5	$239.90	6.368%	$255.1768	$255.18	$255.20	$255.20
Purchase #6	$145.28	3.621%	$150.5406	$150.54	$150.55	$150.50
Purchase #7	$178.81	3.599%	$185.2454	$185.25	$185.25	$185.20
7 purchase totals =	$894.84		$957.2717	$957.29	$957.35	$957.20